Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: mosulll on March 30, 2008, 07:40:33 AM

Title: FPGA outputs
Post by: mosulll on March 30, 2008, 07:40:33 AM

hello. My friend and I are trying to build our first robot. We are trying to use instead of a microcontroller a FPGA, a spartan 3 . I was wondering how we could use, and if of course , the FPGA to put out the signals necessary to command our servos. I tried to use the expansion connectors but after programming the output.. all the pins have the same voltage , even though i tried to make at least some outputs to have a "0" level.

Title: Re: FPGA outputs
Post by: Rebelgium on March 30, 2008, 08:12:37 AM

you'll need to program PWM to the outputs used for servo's.
But ofcourse first you'll have to find what's wrong now...

Title: Re: FPGA outputs
Post by: Kohanbash on March 30, 2008, 11:15:31 PM

When you synthesize the chip are you selecting which pins should be Input and Output

Title: Re: FPGA outputs
Post by: mosulll on March 31, 2008, 05:53:22 AM

Yes, I have selected the pins. I hope I did it right. I've read the user guide, and I think I've chosen the right ones. Though, I still have several questions. On my FPGA there are 3 Expansion Connectors, each one having 40 pins. Pin 1 should be the GROUND and pin 3 should be Vcc (+3.3V) and the other ones should be programmable (I guess...). If I measure the voltage between the PIN3 (+3.3V) and PIN1 (ground), I obtain -0,77 V.. If I measure the voltage between PIN3 (+3.3V) and the ground from the DC adapter, I obtain +2,5 V. My question is what will the voltage for controlling the servo be? I know it might be a very stupid question, but I don't get it...
I'd appreciate if you could tell me where I could find some information about programming the expansion connector.
Thank you.

Title: Re: FPGA outputs
Post by: Admin on April 06, 2008, 12:46:32 PM

Quote

My friend and I are trying to build our first robot.

You should probably stick to the simpler stuff, like a microcontroller . . .

Quote

My question is what will the voltage for controlling the servo be? I know it might be a very stupid question, but I don't get it...

5V (3.3V may work, but will result in potential issues)
http://www.societyofrobots.com/actuators_servos.shtml

Quote

Pin 1 should be the GROUND and pin 3 should be Vcc (+3.3V) and the other ones should be programmable (I guess...). If I measure the voltage between the PIN3 (+3.3V) and PIN1 (ground), I obtain -0,77 V.. If I measure the voltage between PIN3 (+3.3V) and the ground from the DC adapter, I obtain +2,5 V.

It sounds like your grounds are set as common . . .
http://www.societyofrobots.com/robot_faq.shtml#circuit_debug