The idea for this module came from a schematic that has been floating around the web for years - 'beat frequency indicator' The idea is to feed the circuit two signals and depending upon which one had the higher frequency the ring of 4 LEDs would light up in a clockwise or anti-clockwise direction. The speed of rotation would indicate how close or disparate the frequencies are. If the signals have the same frequency then just one LED is lit.
The original circuit used 74xxx series ICs for the logic, so it was simple enough to find the CMOS equivalents (sort of), then add gates corresponding to the LEDs and use the spare outputs of one chip to feed pots to make sequences. Then for good measure a discrete XNOR circuit was added to give a pseudo ring-modulator output based on the 2 incoming signals.
In operation this module is quite unique; the CV signals return to 0 between each step, the length of each step can vary depending on the incoming signals. Gates come in spurts. The circular LED display jerks around, sometimes it completes several revolutions confidently and then stutters between two stages, sometimes it shimmers on one spot.
At both audio rates and clock rates, this module is quite unpredictable but always seems to be putting out useful signals.
PCB = USD18
Panel = USD20
assembled = USD160
Beat Freq panel template - this version of the template has holes to suit 3mm LEDs rather than the windows of the production version.