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I Can't get my HCS_C to work. How do I troubleshoot it?

Good question--I have created a troubleshooting page HCS_troubleshooting to help

with this. In general, I will not be able to do the debugging for you, but I and the

HCS community will help as much as is reasonable. But PLEASE NOTE, I will

repeat: this is a do-it-yourself project, I CANNOT do your debugging for you.

This is something you must expect to do for yourself (or to find a local hardware type

to help you). You must set your expectations correctly for this project--yes, you will

have days where everything goes wrong and you will get frustrated. When that happens,

don't follow with a bunch of worse mistakes, like annoying me or the rest of the HCS

community. We will help you within reason on the Circuit Cellar BBS as long as

you are nice (hard to do when you've got problems, I know)! If you send email (not

preferred for troubleshooting), be prepared to see long waits--I get as much as 500-

1000 emails a day, mostly spam, and will sometimes miss an email or forget about

one you've sent to me. Just be patient, be polite, keep the expectations reasonable,

and I will help you as best as I can.

OK, with that out of the way, go to HCS_troubleshooting for help with HCS_C

problems.

What tools do I need to troubleshoot HCS_C?

You will need a logic probe (pen like tool that indicates a logic 0 or 1), a current limited

powersupply, a low-voltage volt-ohm-meter, and preferably an oscilloscope or logic

analyzer. I designed a handheld logic probe/scope for one of the Circuit Cellar contests,

you can build your own based on a design like this. If I ever get time, I'll write an article

on that project and describe it on this website as well.

How do I connect to HCS_C?

There's a document called the HCS_C Connection Users Manual that goes over this in

detail. In general, remember that HCS_C is a 3.3 volt system--but the IO pins are all

5 volt tolerant. So I recommend for safety that you run everything at 3.3V, but if you

are very careful, you can connect 5V devices into HCS_C. You need to follow some

guidelines to ensure reliable operation of your HCS_C. First and foremost, the buffers

are not intended to drive or receive long signal inputs. If you have the IO protection,

you should be able to reliably operate wires as long as about 5-10 meters, but lines

longer than that (for example, sensors around the house) will accumulate static/conducted

voltage potentials that could seriously damage your HCS_C. Even short lengths are no

guarantee--see the HCS_C Connection Users Manual more more recommendations for

safe and reliable hookup to the HCS_C board. The RS485 and RS232 connections can

safely be connected to 5V modules.

Can I power external circuitry from HCS_C?

Yes. There are ground and power pins on the two IO connectors. Power is 3.3V, do

not hook up 5V power to these connections or you will damage your HCS_C. You

can get about 1A max from these pins (less if you use ribbon cable since ribbon cable is

made of stranded wire about 28 guage). You MUST add a significant heat sink to the

HCS_C 3.3 volt regulator if you do this. The regulator is located next to the power

connector.

What do I do if I'm getting noise on the IO lines?

You must first determine the source of the noise. Don't just stick a capacitor on the

signal, this is poor engineering practice. Noise in the form of signal crosstalk can be

ntroduced on HCS_C IO lines because those connectors do not have alternating

grounds. If this turns out to be the problem, using a shielded cable such as an IDE

disk 40 pin ribbon connector may solve this problem. You should also check that

you have a good grounding setup. In general you want to ensure that the low impedance

path to ground for the IO buffers comes straight from the powersupply and not through

the IO connectors. There is more information about these issues in the

HCS_C Connection Users Manual.

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