Cosmic Ray Detector Manual

01Quickstart

The steps from receiving the detector to your first successful measurement. Follow them in order and see cosmic rays being detected for yourself.

1. Identify the modelby the box shape
2. Unpackunit and cable
3. Connect to a PCUSB cable (a driver on Windows)
4. Measure in the app5 min in Chrome or Edge
5. Save.csv or .dat
6. Checklook at rate and ADC

1. Identify your model

   Tell OWAN (v1) from OHASHI (v2). If there is a sticker on top of the box, a bowl on a young-grass green ground is OWAN and chopsticks on an unbleached kraft ground is OHASHI. Without a sticker, go by the shape of the box (see the photos above, or 02 Models and how it works). The "Both / v1 / v2" switch at the top right keeps only the instructions for your model.

2. Unpack and check the contents

   The box contains:

   • The cosmic ray detector itself
   • A USB cable (for v1 it is usually Type-A to Mini-B) (for v2 the detector end is USB Type-C)

   With an assembly kit you also have to bond the scintillator to the SiPM and make it light-tight. See 10 Assembly.

3. Connect to a PC

   • v1 On Windows, install the CH341 driver first (03 Connect to a PC). macOS, Linux and Chromebooks normally need nothing.
   • v2 No driver is needed. Just plug it in and it appears as a COM (serial) port.
   • Connect the detector to the PC with the supplied USB cable. If the display shows information, the unit is powered. Some units have no display; just go on to the next step.
   • A charge-only cable cannot carry data. If the PC does not see the detector, try another cable.

4. Measure for 5 minutes in the web app

   Use Chrome or Edge on the PC (Firefox and Safari do not support USB serial connections).

   • v2 Open https://accel-kitchen.com/app/cosmicray-monitor/. The first screen asks for your model: choose v2, press "Connect with USB", pick the detector's port and confirm.
   • v1 Open https://accel-kitchen.com/app/cosmicray-monitor/v1. Press "Connect by USB" and choose the detector's port (for example COM3 or /dev/tty.usbserial-XXXX).
   • After a moment the measurement starts and the graphs begin to move. Leave it running for 5 minutes.
   • If the port does not appear in the list, replug the USB cable or try another USB port. If it still does not appear, check the driver (v1 on Windows).

5. Save the data

   • v2 Start auto-save with "Choose a folder", or press "Save .dat" / "Save .csv" to put everything on screen into one file.
   • v1 Press "Save as .csv" (or "Save as .dat") and the file is downloaded to the PC. If you choose a save folder first, the data can also be appended to a file automatically.
   • Open the saved file in a text editor or Excel and check that it contains data. The meaning of each column is in 06 Data and analysis.

6. Check that it works properly

   These values are a guide. If yours are far off, see 09 Troubleshooting.

   Guide for the plastic scintillator version (5 × 5 × 1 cm)

   Item	Normal range
   Count rate	about 0.5–2.0 cnt/s
   Events in 5 minutes	about 150–600 events
   v1 ADC distribution	Out of 0–1023, most values are about 20–200, with an occasional large value above 300
   v2 ADC distribution	0–4095. Ambient gamma rays dominate from just above the threshold up to a few hundred, and the cosmic-ray hump appears around 1000

   If you are inside these ranges, the detector is working properly. You have detected cosmic rays. If you are outside them, use the next table to get an idea of what is wrong.

   Judging from the rate (plastic version, 5 × 5 × 1 cm)

   Rate	Verdict	What to do
   0.5–2.0 cnt/s	Normal	Go ahead and measure
   0.3–0.5, 2.0–3.0 cnt/s	Within the acceptable range	Go ahead and measure. If you are concerned, check the light-shielding and the connector
   0.1–0.3, 3–10 cnt/s	Unclear	Restart the detector and measure again. If nothing changes, check the light-shielding (if the rate is high) or the connector (if it is low)
   Below 0.1 cnt/s	Too low	The threshold is too high, or a connector has come loose (09 Troubleshooting)
   Above 10 cnt/s	Too high	Poor light-shielding is very likely (09 Troubleshooting)

   This guide was checked on the v1. The v2 sets its threshold a little differently, so it may be off (the v2 values will be reviewed once they have been measured).

   The CsI scintillator version (a 1 cm cube) has a much smaller area, so its rate is lower: about one cosmic ray per minute. This table does not apply to it.

7. What to do next

   Once the first measurement works, get the big picture of the research activity. (These pages are in Japanese.)

   • Research Activity ManualOnline tools, the one-year roadmap, weekly reports and mentoring
   • Course materialsThe basics of cosmic rays, radiation and statistics
   • List of past workResearch themes of previous participants

   If anything is unclear, ask on Discord at any time. There is also a weekly office hour.

02Models and how it works

This is a radiation detector that can count gamma rays, beta rays, cosmic-ray muons and more.

How detection works

When a particle passes through the scintillator, the scintillator glows faintly. A SiPM (silicon photomultiplier) turns that light into an electrical signal, and the circuit on the board amplifies it. The microcontroller reads the height of the signal (the ADC value), shows it on the display and sends it to the PC. A larger ADC value means the particle deposited more energy in the scintillator.

1. Particlemuons, gamma rays, etc.
2. Scintillatorglows when hit
3. SiPMlight to electricity
4. Amplifiermakes it bigger
5. Peak holdkeeps the peak height
6. Microcontrollerturns it into a number (ADC)
7. Display and storagescreen, USB, Bluetooth, microSD

If you would like to learn about cosmic rays and detectors from the basics first, read the course material "The basics of cosmic rays and detectors" (in Japanese).

How the signal changes along the way

Between the particle and the number, the shape of the signal changes twice. The amplifier turns the SiPM's tiny signal into a larger, short pulse, and then the peak hold keeps the height of that pulse for a short while. While it is held, the microcontroller reads the height. That is the ADC value.

The "trigger" is the moment the peak-hold output rises above the threshold. The ADC is read next, and finally the circuit is reset to be ready for the next pulse. How the reset works differs by model. v1 simply waits until the signal has decayed below Res.v2 forces a reset with a short pulse (about 20 µs) from the microcontroller's D8 pin.

Names and stickers

v1 is called OWAN (a rice bowl) and v2 is called OHASHI (chopsticks). The sticker that goes on top of the box draws that tool inside a round crest, with particles falling toward it. If there is a sticker, its picture and ground color tell you the model.

v1 A tall box

OWANbowl

Online Watcher of Ambient Natural radiation

A bowl on a young-grass green ground. The steaming bowl catches the particles as they fall.

v2 A nearly cubic box

OHASHIchopsticks

Online Hands-on Analyzer of Scintillation Hits, Individually

Chopsticks on an unbleached kraft ground. The chopsticks pick up a single falling particle.

The drawing and letters are in sumi (ink black); the initials and the seal at lower right are in shu (vermilion). The Accel Kitchen logo runs along the bottom edge. The sticker goes on top of the box (the lid).

How v1 and v2 differ

Parts of the v2

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1. OLED display: shows the count (Cnt), the rate (Rate) and more.
2. LED: flashes every time a particle is detected.
3. RESET button: restarts the detector.
4. Jacks: four of them, OUT and IN1 to IN3. They connect external detectors.
5. Scintillator and SiPM: the block wrapped in black tape. It is wrapped so that no light gets in.
6. Test points: GND1 and TP1 to TP4. This is where you put an oscilloscope probe. TP2 is the amplified signal and TP3 is the peak-hold signal. TP4 is near the trimmer.
7. Standoffs (spacers): they lift the board and leave room underneath for the Nano ESP32.

The front view (a photo of a prototype).

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1. Arduino Nano ESP32: the microcontroller with the USB Type-C port. It plugs into the sockets on the back of the board.
2. microSD slot: put in a FAT32 microSD card and the detector can log by itself.
3. Gain trimmer (blue): changes the gain of the amplifier.
4. Standoffs (spacers): they hold the board up off the floor.
5. Jacks: lined up along the edge of the board.

The back of the board (with the scintillator removed).

The vibration motor is a part you add later. If you connect it directly to the microcontroller pin (A7), the current is too large and damages the microcontroller. Connect A7 → 1 kΩ → an NPN transistor (such as a 2N3904 or S8050) or an N-channel MOSFET (2N7002), and put a diode (1N4148) in parallel with the motor. Do not connect it to D13 (it is shared with the microSD signal, and the log gets corrupted). Noise from the motor can also cause false counts.

What comes with it, and handling

• The detector itself
• A USB cable

Specifications at a glance

For your safety

03Connect to a PC

Connect the USB cable so that the PC can find the detector.

The big picture

USB serial driver

The v1 talks to the PC through a USB-to-serial converter (a CH341-type chip), and some operating systems need a driver for it. The v2's Arduino Nano ESP32 speaks USB directly, so no driver is needed.

ls /dev/tty.*

dmesg | grep tty

sudo usermod -a -G dialout $USER

Connect the USB cable

Connect the detector to the PC with the supplied USB cable. The display on the detector shows information like this. Units without a display show nothing.

From power-on to counting

1. Power onplug in the USB cable
2. Measure the noiseabout 0.1 s (10 samples)about 1 s (100 samples)
3. Threshold is setminimum + 20 (Sig)maximum + 50 (Thr)
4. Logo and settings shownabout 2 s
5. Counting startsCnt goes up

04Measure

Use the web app to turn the detector's data into graphs and save it on the PC.

Measure with a v2

1. Open the app and choose your model

   Open https://accel-kitchen.com/app/cosmicray-monitor/. The first screen asks which model you have. Compare your detector's box with the pictures and choose v2. The browser remembers your choice, so next time you start at the connection screen. The app can show English (switch at the top right).

2. Connect with USB

   Press "Connect with USB", choose the detector's port in the browser's list and press "Connect". When the bar at the top changes to "Connected · USB", you are done. The graphs grow every time a cosmic ray arrives.

3. Measure and save

   For a first try, measure for about 5 minutes. For saving, "Choose a folder" (auto-save) is recommended. Incoming data is appended to <detector name>_<date>.dat. To put what is on screen into a single file, press "Save .dat" or "Save .csv" under "Download".

The model chooser screen

Scroll the screenshot sideways →

1 2 3

1. v1: a tall box. A small window for the display and a small round hole on the top face. This opens the page for the v1.
2. v2: a nearly cubic box. A window for the display and two round holes on a side face. This is the app proper.
3. v2.1: a flat box with posts at the four corners. Its screen is still being prepared and you cannot choose it yet.

The browser remembers the model you chose. To choose again, press "Choose another model" at the top of the connection screen.

The first screen of the app (connect)

Scroll the screenshot sideways →

1 2 3 4

1. Connect with USB: one cable. The most reliable way.
2. Connect with Bluetooth: wireless. In "Detector name", enter the detector's Bluetooth name (initially CosmicRay).
3. Try the demo: no detector needed. Synthetic data drives every feature.
4. Choose the folder first: pick the save folder before you connect.

The screen while measuring

Scroll the screenshot sideways →

1 2 3 4 5 6 7 8 9 10

1. Connection status: "Connected" and the detector's name. The dot flashes each time an event arrives.
2. Pause recording: incoming events are not recorded (the detector keeps counting).
3. Disconnect: the data stays on screen.
4. Oscilloscope: shows the signal waveform (it does not count while you look).
5. Advanced settings: the threshold, switches for the detector's functions and more.
6. Total events, average count rate, elapsed time: the rate is divided by the time with the dead time subtracted.
7. Energy spectrum (ADC histogram): the number of events per signal size. The low hump on the left is ambient gamma rays; the hump on the right (around ADC 1000) is cosmic rays.
8. Count rate over time: how the rate changes.
9. Temperature, humidity, pressure, external detectors, average ADC, dead time, trigger
10. Save: choose a folder and auto-save starts. The format and notes are set here too.

This is the demo (synthetic data). The numbers are not a real measurement.

Measure with a v1

1. Open the app and connect

   Open https://accel-kitchen.com/app/cosmicray-monitor/v1 and press "Connect by USB". Choose the serial port (such as COMx) and the measurement starts by itself after a moment.

2. Check that the graph moves

   Check that graphs appear and that Cnt: on the detector's screen keeps going up.

3. Save

   When the measurement is finished, press "Save as .csv" or "Save as .dat" to download the data to the PC (if you choose a save folder first, the data is appended automatically). A .dat file is tab-separated, and lines that start with # are the header and notes. A .csv file is comma-separated, and its first line is the header. Open it in a text editor and check that it contains data.

   

The first screen of the v1 page (connect)

Scroll the screenshot sideways →

1 2 3 4

1. Connect by USB: one cable. The most reliable way.
2. Connection options: the baud rate (normally 9600) and the board type (normally "Detect automatically").
3. Connect by Bluetooth: wireless. Only the ESP32-S3 version of the detector can use it.
4. Try the demo: no detector needed. Synthetic data lets you try every feature.

The v1 page while measuring

Scroll the screenshot sideways →

1 2 3 4 5 6 7

1. Total events, average count rate, elapsed time: the rate is divided by the time with the dead time subtracted.
2. Energy distribution (ADC histogram): the number of events per signal size. You can change the bin width and switch to a log scale.
3. Count rate over time: how the rate changes.
4. Board: the connected detector (such as Arduino Nano). To its left are the average temperature and the average dead time.
5. Mode: "Single (Master)" means one unit is measuring alone. For coincidence you choose Slave (05 Coincidence).
6. Choose a save folder: auto-save starts from here.
7. Save as .csv: puts the data on screen into a single file ("Save as .dat" is just above it).

This is the demo (synthetic data). The numbers are not a real measurement.

How to save

Everything is in the panel on the right of the measurement app (on a narrow screen, the "Save" button at the bottom right). Once you choose a folder, auto-save starts from there. Use auto-save for long measurements (the screen keeps at most 1 million events).

1 2 3 4 5

1. Choose a folder: auto-save starts from here.
2. Format: .dat, .csv or both.
3. Notes: place, orientation, conditions and so on. They are written at the top of each file, with # at the start of each line.
4. Download: puts the data on screen into a single file.
5. Clear data and start over: also sends RESET to the detector and returns the event number and the time to 0. Files you have already saved are not deleted.

This is the v2 screen. On the v1 page the buttons read "Choose a save folder" and "Save as .dat" / "Save as .csv", and there is also a "File name prefix" field. On the v1 page, "Clear data and start over" clears only the data on screen (it does not send RESET to the detector). On the v1 page, the notes are written to the .dat file only.

• If the browser asks for permission to write, choose "Edit files" (the exact wording depends on the browser).
• Incoming data is appended to <detector name>_<date>.dat. A new file starts when the date changes, and when a file gets very large it is split into _02, _03… The first half of the name is the detector's Bluetooth name, so if you give each unit its own name, the files are separated per unit too (FAQ).
• On the v1 page, "File name prefix" sets the beginning of the file name.
• A file saved with the "Download" buttons is named <name>_<YYYY-MM-DD_HH-MM-SS>.dat (the time you started measuring).
• If you try to close the tab while there is data that has not been written yet, the browser asks you to confirm.

Watch the waveform with the oscilloscope

Press "Oscilloscope" in the bar at the top to see the waveform of the signal coming from the detector. Use it to check that a signal is arriving and that the threshold is right. On the v2 one point is shown every 12 µs. The v1 page has it too. The detector returns to counting by itself if no command arrives for 60 seconds, but the v1 page sends a keepalive every 15 seconds while it is open, so the detector does not return. On a v1 detector one point is shown every 6.5 µs on the Arduino Nano and every 12 µs on the ESP32-S3 version. At 9600 bps the Arduino Nano can send only about 2 waveforms per second. While it is open, all counting stops, including coincidence counting.

The oscilloscope screen

Scroll the screenshot sideways →

1 2 3 4 5 6 7 8 9 10 11 12

1. Counting paused: the time the oscilloscope is open.
2. Triggered / Free-run: capture when the signal crosses the threshold (default), or keep capturing.
3. Rate limit [/s]: the number of waveforms sent per second (1–20, initially 3). Use fewer over Bluetooth.
4. Re-arm (threshold −): how far below the threshold the signal must fall before the next waveform can be captured (initially 5).
5. Persistence: how many earlier waveforms stay faintly overlaid.
6. Fit the vertical axis: off by default (this screenshot was taken with it on).
7. Pause: freezes the current waveform so you can look at it slowly.
8. Clear: removes the overlaid waveforms.
9. Save .wfm: saves the waveform you can see to a file.
10. Waveform: the newest one is the dark line. The red dashed line is the threshold. Drag the handle at its right end up or down, and the position where you let go is set on the detector (after a power cycle it returns to the auto-calibrated value). This is the threshold actually used for counting. You can also move it with the ↑ and ↓ keys (Shift for 10, PageUp / PageDown for 100). The teal dashed line is the re-arm level and moves with the threshold.
11. Peak ADC, number of waveforms and so on: numbers for the waveforms you can see now.
12. Close and resume counting

This is the demo (synthetic data).

What you see is not the raw amplified pulse but the output of the peak-hold circuit. It rises, stops at the peak, falls slowly and is then reset. To see the raw pulse, put an oscilloscope probe on the board's test point (TP2) (10 Assembly).

How it captures (Triggered / Free-run) and re-arm

• Triggered (default): a waveform is captured only when A0 crosses the threshold. After one is captured, the next one waits until A0 has fallen back to the re-arm level or below.
• Re-arm: the level is "threshold − the value in the box" (initially 5; if the threshold is 120, the level is 115). It is drawn as a teal dashed line and moves with the threshold line when you drag it. If you empty the box and leave it, it returns to the default of 5.
• Free-run: without waiting for a trigger, it keeps capturing the newest window of 161 points at the interval set by the rate limit. Use it to look at the baseline or the noise, or to look for small signals that never reach the threshold. The vertical trigger line disappears and the horizontal axis becomes "time within the window".

The v1 page's oscilloscope has the same Triggered / Free-run switch and "Re-arm (threshold −)". On a v1 detector it works once you have re-flashed the updated sketch.

Advanced settings

Press "Advanced settings" in the bar at the top and a panel opens from the right. The table of contents at the top of the panel jumps to each section. You can change the board's settings only while a detector is connected. The "Board: …" lines show the values the detector is using now (the "Advanced settings" of the v1 page has "Thresholds and mode", "ESP32-S3 settings", "Connection" and "Help").

Trigger and thresholds

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1. Trigger mode: Analog, Digital or Dual. At power-on it is always Analog.
2. Signal threshold (0–4095): used in Analog and Dual. Even if you set it by hand, it goes back to the auto-calibrated value when you power the detector off and on again.
3. Auto-calibrate: measures the noise for about 1 second (100 samples) and sets the threshold to its maximum plus the margin (initially 50). Press it with no light getting in. If you change the margin, the new value is saved.
4. Comparator threshold (PWM duty, 0–255): used in Digital and Dual.
5. Auto PWM: moves the threshold and settles where the noise triggers no more than the target number of times (about 8 seconds). Run it once after you switch to Digital or Dual.

If the threshold is too low, noise gets counted too; if it is too high, small signals are missed. When in doubt, stay in Analog and use auto-calibration.

Besides these there are "Display" (how often the graphs are redrawn: 1 s, 3 s, 10 s or manual), "Server upload" and "Help".

Other features of the app

For details that are not in this chapter (all the commands, the file formats, the pin map), see the measurement app's manual.

While you measure

• Do not touch the board directly while measuring.
• Make sure the USB cable is not coming loose and the PC does not go to sleep. Either one can leave gaps in the data.
• How long to measure, and the settings for an overnight run, are in 07 FAQ.

v2Measuring without a PC

05Coincidence

Stack two detectors and pick out only the events in which both respond at almost the same time.

What is a coincidence measurement?

Stack two detectors one above the other and record only the events in which both respond at almost the same time. Noise that arises inside a scintillator, and natural radiation such as gamma rays, reaches only one of them. That lets you pick out efficiently the cosmic-ray muons that pass through both detectors.

For an overview and an example of the connections, see also the explainer video (in Japanese).

If one unit measures about 1 cnt/s, the rate drops sharply in a coincidence measurement (it depends on the distance between the detectors and their area). To collect enough events you have to measure much longer than with a single unit. The rate is often around 0.01–0.1 cnt/s, so it can take several hours.

v1Link a Master and a Slave

v2Connect OUT and IN

06Data and analysis

What is inside the saved files, and how to begin analyzing them.

What the data contains

The detector outputs one line every time an event occurs: a row of numbers separated by spaces.

### Event Time[ms] ADC[0-1023] SiPM[mV] Deadtime[ms] Temp[C]

### Event Time[us] ADC[0-4095] Deadtime[us] Temp[C] Hum[%] Press[hPa] Dig1 Dig2 Dig3 Ana1 Ana2 Ana3
42 18732450 1940 1203000 24.3 48.2 1013.2 1 0 1 2448 112 2804

How to work out the count rate

Divide by the time with the dead time (the time it could not count) subtracted. Do not divide the number of lines you received by the elapsed time.

Dead time includes the time spent processing one event, rewriting the display, having the oscilloscope open and so on. On the v1, processing times shorter than 1 millisecond are rounded down, so it is mostly the time spent rewriting the display and the oscilloscope time. The rate is the number of events divided by the live time.

rate [events/s] = (last Event − first Event) ÷ ((last Time − first Time) − (last Deadtime − first Deadtime))

Time and Deadtime are in milliseconds for the v1 and microseconds for the v2. Make the units match before you calculate. On the v2, if Event, Time or Deadtime goes down because of a RESET or a restart, start a new segment there and add the segments together.

How to read a histogram

A histogram (an energy distribution) counts your data by signal size (ADC value) and plots the result. With a plastic scintillator, a gamma-ray hump on the weak-light side and a cosmic-ray hump on the strong-light side separate clearly.

Besides "ADC histogram", the analysis page has two more tabs. Zenith angle (the zenith angle distribution): enter the count rates you measured with the detector tilted in steps of 15°, and it fits them with cosnθ. Energy calibration builds a formula that converts the ADC value to keV from the peaks of a source's known gamma rays. If one file holds several measurements (separated by a RESET or a restart), the analysis page splits them apart and adds them together.

import pandas as pd

cols = ["event", "pc_time", "time_us", "adc", "deadtime_us",
        "temp", "hum", "press", "dig1", "dig2", "dig3", "ana1", "ana2", "ana3"]
df = pd.read_csv("CosmicRay_2026-10-22.dat", sep="\t", comment="#", names=cols)

live_s = (df.time_us.iloc[-1] - df.time_us.iloc[0] - (df.deadtime_us.iloc[-1] - df.deadtime_us.iloc[0])) / 1e6
rate = (df.event.iloc[-1] - df.event.iloc[0]) / live_s
print(f"{rate:.2f} cnt/s")

import pandas as pd

cols = ["event", "time_us", "adc", "deadtime_us", "temp", "hum", "press",
        "dig1", "dig2", "dig3", "ana1", "ana2", "ana3"]
rows = [l.split() for l in open("LOG0001.TXT") if not l.startswith("#")]
rows = [r for r in rows if len(r) == 13 and r[0].isdigit()]
df = pd.DataFrame(rows, columns=cols).apply(pd.to_numeric, errors="coerce")

import pandas as pd

# when you saved a .csv (comma-separated, with a header row)
df = pd.read_csv("data.csv", comment="#")

# when you saved a .dat (a # header and tab-separated)
cols = ["event", "pc_time", "time_ms", "adc", "sipm_mV", "deadtime_ms", "temp", "mode"]
df = pd.read_csv("data.dat", sep="\t", comment="#", names=cols)

Analyze it in Google Colaboratory

Google Colaboratory is a free service that runs Python in your browser. You do not need to install Python on your PC; a Google account is all you need. In the exercises you analyze sample files and try out various kinds of cosmic-ray analysis. If you work through them while measuring for yourself, you will see how to apply them to your own research. The exercises are written in Japanese.

• Exercise 1How often do cosmic rays arrive?
• Exercise 2How various factors correlate with the detection rate
• Exercise 3Change the conditions, measure, and look at the trend
• Exercise 0 (optional)Introduction to Python: your first programming
• Exercise 4 (optional)Advanced analysis: comparing data sets and statistical tests

Copy a notebook to your own Google Drive

1. Open an exercise link in your browser. You must be signed in with a Google account to work. If you see Sign in at the top right, sign in with your own account.

   

2. From the File menu at the top left, choose Save a copy in Drive. The notebook is copied to your own Drive and you can edit it freely.
3. The structure of the data files and how to analyze them are explained inside the notebook. Try different things.

Basic Colab operations

• Run a cell: press the ▶ button to the left of the cell, or press Shift + Enter.
• Top to bottom: run the cells in order from the top. Running only a cell in the middle may give an error.
• If you get an error: first try "Runtime" → "Restart runtime", then run the cells again from the top.
• Loading data: to use data on Google Drive you first have to mount (connect) the Drive. Follow the instructions in the notebook.

07FAQ

If something is unclear or you are stuck while working on your research, look here first.

SETUP

MEASURING

DETECTOR SETTINGS

Glossary

OWAN / OHASHI

The names of the detectors: v1 is OWAN (a bowl) and v2 is OHASHI (chopsticks). The sticker on top of the box carries the name and the picture.

Scintillator

A material that glows faintly when a particle passes through. In this manual it is a block of plastic or CsI.

SiPM

Silicon photomultiplier. A component that turns very faint light into an electrical signal.

Muon

A particle made when a cosmic ray hits the atmosphere. It is the main component of the cosmic rays that reach the ground.

ADC

The height of the signal turned into a number: 0–1023 on the v1, 0–4095 on the v2. The larger it is, the more energy was deposited.

Peak hold

A circuit that keeps the height of a pulse's peak for a short while. While it does, the microcontroller reads the height.

Threshold (trigger)

The line that says "count signals from this size upward as particles". When a signal crosses it, that is the trigger.

Dead time / live time

The time it could not count and the time it was counting. The rate is divided by the live time.

Count rate (cnt/s)

The number of events counted per second.

Coincidence

A way of measuring that keeps only the events in which two or more detectors respond at almost the same time.

Histogram

A bar chart made by counting the data by signal size. Also called an energy distribution.

Web Serial API

The mechanism by which a browser opens a USB serial port. Chrome and Edge support it.

BLE (Bluetooth LE)

Low-energy Bluetooth. The v2 uses it to connect to the measurement app.

Firmware / sketch

The program that runs inside the detector's microcontroller. In Arduino, a program is called a "sketch".

08Firmware

"Firmware" is the program that runs inside the detector's microcontroller. How the signal is read, how the threshold is chosen and the format of the output data are all decided by it.

Which sketch to flash

The measurement app supports the v2 sketch in this table (the end of the measurement app's manual also lists it as the "supported firmware").

The oscilloscope's "Triggered" / "Free-run" switch and "Re-arm" need a sketch dated 2026-10-23 or later. An older sketch still counts, but these two settings have no effect (with an old sketch the v1 page shows "This firmware does not support the oscilloscope."). Check that the sketch you flash is the new version.

How to flash it

Common preparation

1. Install the Arduino IDE: get it from the Arduino download page (Arduino IDE 2.x).
2. Install the libraries: open "Sketch" → "Include Library" → "Manage Libraries…" in the menu, then search for and install the following.

Threshold

The threshold is the line that says "count signals from this size upward as particles". If it is too low, noise is counted; if it is too high, small signals are missed. Either way, it is set automatically every time you power on.

With a high threshold like ③, small gamma rays are no longer counted. Decide according to what you want to count. When in doubt, use the automatically chosen value.

Commands

You can read and write the settings by sending commands to the detector. The buttons of the measurement app send these commands behind the scenes. To send them by hand, use the Arduino IDE's serial monitor (9600 baud, line ending LF or CR) or the app's "Advanced settings". One line is one command, and at most 31 characters for the v1.47 characters for the v2.

v1 The v1's settings are not saved. After a power cycle the thresholds go back to being set automatically. The oscilloscope settings (rate limit, capture mode and re-arm) are not saved either, and go back to their initial values after a power cycle. If no command arrives for 60 seconds, the oscilloscope turns itself OFF and counting resumes (but the v1 page sends a keepalive every 15 seconds while it is open, so this does not happen there).

v2 Settings that stay: the PWM value, the auto-calibration margin, the on/off state of the features, the buzzer and vibration settings and the Bluetooth name. Settings decided again at every startup: the signal threshold (auto-calibration) and the trigger mode (always ANALOG). The oscilloscope settings (rate limit 3, capture mode Triggered, re-arm 5) also go back to their initial values at every startup. While a command is running the detector does not count, and that time goes into the dead time (auto-calibration takes about 1 second and AUTO_PWM about 7–8 seconds). Commands are case-sensitive, and a line that is too long (more than 47 characters) is discarded. The list of all commands and the pin map are in the appendices of the measurement app's manual.

09Troubleshooting

Find the cause and the remedy from the symptom. If it does not get solved, ask a mentor on Discord.

First, find your symptom

• The rate is too high (above 10 cnt/s)CAUSEOutside light is getting inREMEDYReinforce the light-shielding. Look for gaps in the tape.
• The rate is too low (below 0.1 cnt/s on the plastic version)CAUSEThe threshold is too highREMEDYRestart with no light getting in (unplug and replug the USB cable).
• ADC stays at 0CAUSEThe connector to the upper board (the SiPM board) has come looseREMEDYOpen the case and reconnect it.
• ADC stays at the maximumCAUSENot enough light-shieldingREMEDYReinforce it with aluminum or black tape.
• The data breaks off, or event numbers jumpCAUSEThe USB cable, or the PC went to sleepREMEDYReplug the cable. Turn off sleep.
• The port cannot be foundREMEDYTry the checklist below, from the top.

When the port cannot be found

1. USB cableIs it a cable that carries data, not a charge-only one? Try another cable.
2. USB portTry plugging it into another USB port.
3. Driver (v1 on Windows)Is the CH341 driver installed? After installing it, restart the PC (steps).
4. BrowserAre you using Chrome or Edge? Firefox and Safari show no list of ports.
5. Other applicationsIs the Arduino IDE's serial monitor, or another browser tab with the app open, using the port? Close it and try again.
6. Ask a mentorTell them on Discord about the symptom and what you have tried so far.

Hardware problems

Software problems

What to tell us when you ask for help

10Assembly

How to assemble the assembly kit. If you received a finished unit, you do not need to read this.

The assembly sequence

1. Scintillatorwrap → grease → shield
2. Displaysolder it upright
3. Main boardlow parts first; the Arduino from the corners
4. Join the boardsscrew them together
5. Check with a scopeTP1 to TP3
6. Flash and finishsketch → case

1. Scintillatorwrap → grease → shield
2. Sockets, etc.solder by hand
3. Stack the boardswith spacers
4. Nano and OLEDplug into sockets
5. Check it worksOLED and app
6. FirmwareArduino IDE
7. Caseprint and assemble

The scintillator and the SiPM board (v1 and v2)

1. Wrap the scintillator in aluminum foil

   Wrap the whole thing with the shinier side of the foil on the inside. Leave the middle of one face open so the SiPM can sit against it (it is a good idea to leave the opening wider than in the photo).

   

2. Attach the connector and spacers to the SiPM board

   Solder the 6-pin connector to the board, then screw on the spacers.

   

3. Put optical grease on the SiPM

   Spread grease on the light-receiving surface of the SiPM and press it against the window you opened in the scintillator's wrapping.

   

4. Wind the light-shielding tape

   Wind light-shielding tape all the way round to finish. Wind it so that every part has 2 layers or more. Leave the spacers and the 6-pin terminals sticking out. After winding the tape, poke holes for them with a screwdriver or similar.

   

The v1 main board

The display

Solder it so that it stands vertical when seen from the side.

The main board

Solder it following the finished picture (the photo below).

1 2 3 4 5 6 7 8 9 10

1. Arduino Nano: plug it into the board and solder it.
2. USB port (Mini-B): the Arduino Nano's connector.
3. LED (LED1): mind its orientation. Fit it so that it sticks out beyond the board.
4. 3.5 mm jack: the coincidence cable that links two units plugs in here.
5. Reset switch (RESET1)
6. Temperature sensor (TMP36): a half-moon shape with 3 legs. Mind its orientation.
7. BNC connector
8. 2 × 3-pin socket (J2): the SiPM board's 6-pin connector plugs in here.
9. 4-pin socket for the OLED
10. Test points: TP1 to TP3 and GND1 (lined up at the lower right).

The finished main board.

• Watch which side is the front and which the back, and the orientation of the parts.
• Fixing parts in place with cellophane tape before soldering keeps them from shifting.
• Mind the polarity of the LED (the + side has a round electrode, the − side a square one).

The Arduino

First, fit the Arduino so that it does not sit raised. Pins that are tilted may not go into the board, so with the Arduino plugged in, solder the 4 corners on the front and then the 4 corners on the back, checking one pin at a time that it is not tilted. Then solder the rest all together.

The other parts

• Fit the low parts first.
• Mind the orientation of the LED and the temperature sensor (the half-moon shaped part with 3 legs).

Check that it works

1. Join the SiPM board to the main board and screw them together.

   

2. Check the signal with an oscilloscope. Put the probe tip (the core) on TP2 and the ground clip on GND, and look at the pulses. TP1 is the raw SiPM signal, TP2 is the amplified signal and TP3 is the peak-hold signal.

   

   

3. Flash the sketch following the steps in "08 Firmware", put it in the case and you are done.

   

The v2 readout board