Hi,
I’ve a VM140 board which I am using to interface with an 8 channel controller for a polychromatic acousto-optic modulator. The wiring is through a female 25 pin connection (DB25) which has pins for analog voltage control and TTL inputs for blanking the laser lines. I’m running the VM140 with open source software, Micromanager. I’ve wired a DB25 connector and I’ve been testing just the board without the controller using a multimeter.
The analog outputs work nicely and I can use these to control the voltage and hence laser intensities.
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From several other postings on this forum, I believe I’ve digital outputs properly configured but perhaps I’ve totally misread several diagrams and posts…the VM140 digital output clamp and the pins on the DB25 connector corresponding to the TTL inputs into the controller are connected to the positive side of an external power source. The ground from the VM140 digital outputs is connected to the negative side of the external power source. Each of the VM140 digital output channels is wired to the pins in the DB25 connector which correspond to the individual grounds each of the eight channels.
Configuration sound OK? -
When I switch TTL high and measure between a TTL input pin and the ground pin for corresponding channel, I observe approximately the voltage of the power supply minus ~0.6V, which I think is OK from what I’ve read about the VM140 digital outputs.
Is this appropriate? -
The problem arises with TTL low. Just for testing purposes, I initially set this up using a 9 volt battery and low setting produces ~0.5 V and high setting produces ~8.3V when measured as described above.
For a permanent solution, I switched to a 4.5 V AC adapter which gives a TTL high signal of ~4V and should be OK for my purposes. But strangely, the TTL low is either 2V or ???V (my multimeter acts as if there is no input at all) depending on the orientation of the AC adapter when inserted into the electrical outlet. The AC adapter voltage measures ~4.6V no matter the orientation. I assumed this was a problem with my AC adapter and tried another, but I get the same result.
For the controller, no TTL input or high input does not blank the lasers, so obviously cycling between 2V and 4V or “No input” and 4V is probably not going to work for my needs.
I know the max is 50V/100mA for each digital output, so please note that the AC adapter is 1 Amp output. But this shouldn’t be a problem as long as the impedance of the controller inputs (or the multimeter in this case) is high enough, right?
Is this where I messed this one up?
Thanks for your time and any suggestions.
Best regards,
George