A simple circuit question

All,

Excuse my ignorance, but I am looking for some assistance. We are attempting to use a TTL signal to trigger some data acquisition equipment. The sensor is powered by a 5 VDC source (3 A). When we run the sensor output into an oscilloscope, we see the TTL pulse appear, at the proper 5 V level.

However, when we tee this signal off and connect it to the timing box (this handles the triggering and other tasks), the voltage on the TTL output drops down to 1 V, which is insufficient to trigger the system.

So, my question is, what is it about connecting the TTL line to the timing box that 'draws down' the voltage so much?

Thanks for any tips,
D. hill.

It sounds like the sensor can't supply enough current for the TTL input, do you have details (such as the circuit) of the sensor?.