Breadboard stray capacitance issues

Nov 24, 2003 1 Replies

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Hi All,

I like to use breadboards for developing robots because of ease of making changes. But I'm having a bit of a problem of late.

I'm running a pulse accumulator PIC chip on a breadboard which requires an external 50Mhz resonator, also on the breadboard. The chip functions correctly at times and others it doesn't. I'm wondering if the stray capacitance of the breadboard looks like a big low impedance path for that

50Mhz signal from the oscillator and it's going everywhere on the breadboard, causing all sort of false triggers, noise and such on the pulse accumulator.

I suppose one way to find out is to build the circuit on a PCB with all components soldered and/or socketed to isolate the resonator from everything but I wanted people's opinions first. Thanks.

-Dave

Hi Dave, you are saying "breadboard". Neither the whiteboards, nor the cheapo protoboards from Radio Shack/etc, are very good at high frequencies. With the whiteboards, there is a lot of stray capacitance coupling between adjacent rows of pins [15-20 pF range], and the RS/etc boards are made from bakelite or phenolic/whatever, and have very poor high-frequency characteristics. I find these boards to be poor operators above 10 Mhz or so. I have an RS board setup to plug in std 14-pin sized oscillator chips up to 100 Mhz, and the signals go into the mud for higher frequencies. If you want to prototype at higher frequencies, look for protoboards made from std FR4 pcb material.

- dan michaels

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Breadboard stray capacitance issues

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