We would like to record the timestamp when a flash goes of. Can we connect a LDR directly to an analog port of the the VM110 and record when the resistance is high/low enough to open/close the port? Or is there a better solution to use the VM110? Or is there a another Velleman project perhaps better adapted to our needs?
In the past we tried connecting a flash slave-synchro device, but the voltage pulse of the synchro device is too low to record. We could record this on our 'scope but for operational reasons, we prefer a VM110 based solution.
You can use the analog input.
Connect the LDR between A1 and A2 input terminals.
Remove jumper SK2 and keep jumper SK3 installed.
By doing this, the A2 terminal will output +5V as a supply for the LDR.
If the nominal resistance of the LDR is 10k, you should put a 10k fixed resistor between A1 and GND terminal to get the reading to fit in the middle range (of 0…255).
You can use A1 input to detect high voltage when the flash is “on”.
You can test this with the demo software.
The pulse must be 20ms or longer to be detected by the input.
The analog input sampling interval is about 20ms.
If your flash pulse is too short for those 20 ms, a relatively simple circuit based on a 555 timer could provide a long enough pulse. If memory serves, the 555 only needs 10 nanoseconds to trigger and can convert that into any pulse length, you need.
ETA:
I’ve done some tests using a photo transistor and a normal camera flash apparently creates way too short of a pulse to be detected reliably with the K8055.
So here is an implementation of that flash detector using a photo transistor:
Using 47K for R1 and a 0.47μF for C1, the 555 will give off a pulse of about 24ms when it detects a flash. The LED and its current limiting resistor are optional, but nice to have to adjust the light sensitivity with the POT R2.
Here is a prototype setup of the circuit done on the good old RadioShack SensorsLAB:
This setup uses a 2N3904 as Q2 for the K8055 input, so that a detected flash results in a 24ms ON at the input port. The flashes are generated by a Velleman K5300 stroboscope and the K8055 never misses a beat.
I might actually go get another photo transistor and build a permanent setup for this one. This would be handy to measure the pulse rate of my K5300.
