common ground required?
coder1024
Posts: 9
Was hoping someone could give me a sanity check on this.· I have the BASIC Stamp HomeWork Board·and am attempting to receive data from a separate circuit.
My interface between the BASIC Stamp board and this other circuit consists of a data line and a clock line (and a third line I'm watching to signal data availability) and I'm using the SHIFTIN command to read the data.
The other circuit has its own power supply.
My question is as follows.· Are both circuits required to operate from the same power supply so they'll have a common ground?· I'm wondering if powering the BASIC Stamp from its 9V battery and this other circuit from its·batteries is causing a problem since they're not sharing the same ground.
i.e., since I'm using TTL signals to communicate between the microcontroller and the separate circuit, must the ground be common?
·
My interface between the BASIC Stamp board and this other circuit consists of a data line and a clock line (and a third line I'm watching to signal data availability) and I'm using the SHIFTIN command to read the data.
The other circuit has its own power supply.
My question is as follows.· Are both circuits required to operate from the same power supply so they'll have a common ground?· I'm wondering if powering the BASIC Stamp from its 9V battery and this other circuit from its·batteries is causing a problem since they're not sharing the same ground.
i.e., since I'm using TTL signals to communicate between the microcontroller and the separate circuit, must the ground be common?
·
Comments
They can be powered by separate batteries/PSUs, though.
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I was thinking one possibility would be to just power the second circuit from the BASIC Stamp board, however, this would require changing around the other circuit due to its power requirements.
Is there an easy way to make the ground common for these? I can't just connect the ground terminals from both circuits together can I?
You asked:
"I can't just connect the ground terminals from both circuits together can I?"
And the answer to that is:
You sure can, and that's the whole point and purpose of a common ground. You're not supplying power, you're only offering a common ground _reference_.
Remember that the definition of "voltage" is a difference in potential. Without knowing what ground is (voltage-wise), one can not know what the voltage is. Once the grounds are common, everyone is on the same page, and voltages that are in common become readily apparent, amongst and between the attached devices.
Regards,
Bruce Bates
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Post Edited (Bruce Bates) : 6/28/2006 12:18:57 PM GMT
Now, connecting the PLUS sides of the supplies would be a bad thing to do, but you knew that already.