Andy,
You can use an NPN transistor (2N3904 or 2N222A or whatever) and a
couple resistors to boost the Pi signal to 5V. Pi output through a 10K
resistor to Base, Emitter to Gnd, counter fed from Collector, Collector
also tied to 5V through a 1K resistor. Should work up to about 1 MHz.
On 12/30/15 2:54 PM, Andy Tefft wrote:
Initial quick tests are good with one exception - I had just connected an
AVR output to one of the pins on the reset button on the counter and the
AVR was able to toggle that output and reset the counter (pretty sure I was
powering the AVR with 5V). This same trick does not work with the pi,
presumably due to its puny little 3.3v-level outputs. Anyone have a
standard, simple go-to for interfacing between old TTL circuitry and a pi
or something like it?
--
David Forbes, Tucson AZ
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