help with interfacing Arduino with a device re: TTL control

Hi... this may seem like a trivial question but here goes:

I'm trying to work with a device that has a number of inputs. The one input trigger port I'd like to work with is internally pulled high with a pull-up resistor. According to the vendor, if I can pull it low (i.e. to ground) and then let it go high again, the trigger will then fire as it is designed to go on the rising edge.

I'm trying to figure out how to do this - I can tie the trigger line to an input on the Arduino and read it - it reads 5V... so I think what I want to do is somehow pull that low to 0V using the Arduino and then release it again...

Any advice on how to do this?. I had read some stuff about open-collector and doing this by mapping the pin as an output line but that didn't seem to do anything...

Thanks

Set the arduino pin the trigger is connected to output and then setting the pin LOW should pull it to ground.

cyclocrossguy:
Hi... this may seem like a trivial question but here goes:

I'm trying to work with a device that has a number of inputs. The one input trigger port I'd like to work with is internally pulled high with a pull-up resistor. According to the vendor, if I can pull it low (i.e. to ground) and then let it go high again, the trigger will then fire as it is designed to go on the rising edge.

I'm trying to figure out how to do this - I can tie the trigger line to an input on the Arduino and read it - it reads 5V... so I think what I want to do is somehow pull that low to 0V using the Arduino and then release it again...

Any advice on how to do this?. I had read some stuff about open-collector and doing this by mapping the pin as an output line but that didn't seem to do anything...

Thanks

Sounds to me like you can just wire it to an arduino pin set to output mode and set it's value HIGH or LOW as required for your software logic application. You should read the actual 'pull-up' voltage value with a volt meter to make sure the value is close to +5vdc. If it's at some other logic voltage, say 3.3vdc then a series resistor may be required to insure excess current does not flow. It the pull-up voltage is in excess of +5vdc then a switching transistor may be used between the arduino output pin and the external device.

Lefty

Thanks guys - I'll give that a shot then