Monday, June 4, 2018

Measuring film camera shutter speed with Beaglebone Black

Here is a simple circuit utilizing the ADC input on Beaglebone Black to measure camera shutter speed.

A photoresistor is used to detect the light when shutter open, and hence changing the values read by ADC pin P9_40.  The push button is used to trigger the Python script to start reading the ADC input.

Testing on breadboard and the final build on through-hole board:

Note that this is by no mean an accurate measure of absolute shutter speed.  The response time (rise/fall) of photoresistor will affect the result (see the graph below).  Nevertheless, it is useful to compare different shutter speeds.

Source code is available on Github.

Quick start:

git clone
cd bbb-adc-measure
python3 -m venv venv
. venv/bin/activate
pip install -r requirements.txt
python -t 10 > result.csv

Plot the output using gnuplot:

set mxtics 10
set grid
plot 'result.csv' with lines

Here is an example output of measuring 1/15 and 1/8 shutter speeds of my Pentax MX.