help controling a rc servo with a cRIO

[sopraa]

I have run 5 volts through the Vsup, and the scope shows the same "offset" as with 7v.  The pulse is created but its only goes from about 2.5 v to 5 volts.  The power coming out of the 9474 to the servo is about 5 volts,and I got a reading of ~ 2.8 V coming out of the DO port to the servo.  It appears as if there is an offset almost, because I can change the input voltage and the peek rises but the base of the pulse stay still at abotu 2.5V.

Thanks,

Andy

[Brian_R]

Andy,

I'm working on getting a project going here.  If I can confirm that this isn't expected behavior, you will have to call in and return your module for repair.

Thanks!

[sopraa]

Thanks with your help so far Brian,

I have gotten it to work with a FUTBA servo so I am going to adjust my project to use FUTBA servos for now and keep this in mind for the future.  However, I do not think that the module is broken since it works fine expect with the Hitec servos are attached.  If I have time in the future I may try and trouble shoot this problem. 

Thanks,

Andy

[Brian_R]

I have created a simple FPGA program that just writes T then F to DO0.  I was able to have the card produce a 0 to 5 V square wave with a 5 V input.  If you place the negative terminal of a multi-meter on COM (pin 9 on the 9474) and the positive lead on DO0 (pin 0 on the 9474) and it does not get close to zero, you have a broken card.  I have attached the project that I used for debugging.

Your other servo may be working because it uses a non-TTL spec signal. 

Message Edited by Brian R on 08-02-2007 04:11 PM

[sopraa]

I ran the code you sent me and I got 5 volts out.  I think it has something to do with the fact that the modules says you should only use a sinking device with it.  I have tried pulled down resistors and a few other ideas which gets it close but not working  correctly. 

Thanks,

Andy