TTL and med associates

Taylor

Hi everyone,

After spending hours of figuring things out, I realized that the TTL's med associates sends out are opposite from what most pulse generators need (i.e. when my output is on it's grounded and when it's off that's when there's 5 V). I've been told this is a common thing dealing with med so I didn't know if anyone had any experience with this and what the best approach for it would be. I thought about trying to play with some ways to code around it or maybe look and see if I can change it on the PulsePal itself.

But basically I need a TTL from a cue light to then trigger the pulse pal, but the TTL's in med are opposite (sorry if my language about electronics is still off) so it's not triggering the pulse pal.

Update: I have tried fixing the med code and now when the pulsepal is hooked up and the med boxes are on the Trigger Channel 1 light will turn on but it is still not sending a pulse to the output channel

Thanks!
-Taylor

Josh

Hi Taylor,

With Med Associates equipment, definitely make sure that the output signal has the polarity and voltage range you need to trigger Pulse Pal.
On an old Med Associates assay, I remember that the standard logic signal was something like -28V with respect to signal ground. If this is true for your system, it presents two issues:

1.
The voltage is above Pulse Pal's trigger channel range of +3V to +5V (see Pulse Pal specs here). Over time, using a higher voltage can damage the optoisolator.
2.
The voltage is negative, and needs to be positive

The first issue can be solved by creating a voltage divider with two resistors (e.g. this).
The second can be solved by simply reversing the leads. This works because Pulse Pal's trigger channels are optically isolated.

If you're seeing the trigger channel LED light up, you have the correct polarity and Pulse Pal has received the trigger signal. I'd check the trigger link parameters of your output channels, to make sure they're configured to respond to trigger channel 1.

Please let us know if this helps!

-Josh

gunes

Hi Taylor,

I am trying to trigger the pulse pal from the med pc box and having the same problem. I see that you fixed this issue by changing the Mad pc code. Do you mind sharing what you did?

Thanks!
Gunes