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I designed a board to interface the CEL MeshConnect Mini Zigbee module with a lighting controller board. The Zigbee module is able to transmit bytes via UART and I've verified this, but the radio does not receive a response unless I have my oscope or voltmeter probe attached to that pin(and the ground reference of course).

Does this mean I have a grounding issue? Has anyone ever seen this happen before?

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    \$\begingroup\$ Can you post a schematic of your circuit? \$\endgroup\$
    – Chris Laplante
    Aug 16, 2013 at 19:28
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    \$\begingroup\$ What if instead of the ground reference you use two probes and no ground (with scope in "X-Y" mode?). Or what if you just connect the ground only but not the probe; does that make it work? The thing to determine is whether probe capacitance does something, or whether there is some grounding issue. What if you connect one or two digit picofarad range capacitor across the same points? \$\endgroup\$
    – Kaz
    Aug 16, 2013 at 19:30
  • \$\begingroup\$ Unfortunately, I'm using the DSO Nano V3 as an oscope and it uses a single channel. I've tried just connecting ground and that doesn't do anything. \$\endgroup\$
    – Justin Manuel
    Aug 16, 2013 at 19:38
  • \$\begingroup\$ Do you have a good 0V connection between the modules? \$\endgroup\$
    – Spoon
    Aug 16, 2013 at 22:41

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Is this chip on a socket?, pin may be bent under so it only contacts due to probe pressure.

Probe is loading the circuit, missing pullup or RC network.

Probe is acting as antennae?

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  • \$\begingroup\$ To differentiate the mechanical pressure or electrical loading issues, try pushing with an insulated probe (piece of metal stuck in a ballpoint pen housing? though that's probably bad from an ESD perspective) for the first, and soldering on resister of various values to ground for the second. \$\endgroup\$
    – Chris Stratton
    Aug 17, 2013 at 17:07

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