VL=VS?

Lynxmotion Electronics & Software
1

This is a question that has been bugging me for a few days. I have an older SSC-32 (with RS-232) that I have been using with two power supplies. It is connected to an IOIO board whose power is coming from the VL pins on the SSC-32. And it communicates to the SSC-32 via the TTL serial inputs. So far so good.

I decided to try to use a single power supply (it is a 5A power supply pushing 5 servos) so I strap VL=VS. The IOIO board still lights up, the SSC-32 still lights up. But the TTL serial port doesn’t seem to receive anything from the IOIO board. If a rejumper the SSC-32 back to RS-232, the SSC-32 is able to communicate directly to my PC. If I remove the VL=VS jumper and put two different power supplies and switch the SSC-32 back to TTL, the IOIO can talk to the SSC-32 again.

So I’m wondering if anyone knows what could be wrong? My guess is possibly a problem with a shared ground between the IOIO and the SSC-32?

Any thoughts, anyone?

2

OK. I verified that it IS NOT a shared ground. I hooked up the IOIO to separate power, but kept the SSC-32 on VL=VS… and no communications seems to be getting to the SSC-32. So my only conclusion is that the VL=VS strap causes problems with the TTL input on the SSC-32. Has anyone seen this problem?

3

Hi,

We recommend to remove the VS=VL jumper and use two separate power supplies for logic and servo when using the old version of the SSC-32.
We have noticed that communication problems occur when the jumper VS=VL is ON. The reason is the absence of some decoupling capacitors which we’ve added on the SSC-32U version.
The issue is now fixed with SSC-32U.

4

Thanks. I suspected as much. I’ll probably end up buying an SSC-32U anyway. It’s about time.