Yet another homebrew frequency counter... - UK Vintage Radio Repair and Restoration Discussion Forum

MrBungle · 29th Dec 2016, 12:43 am

Decided contracting everything out to a PIC felt like cheating. Plus I don't enjoy playing with MPLAB's toolchain. Ergo, a 1970's magazine style counter is in development. I'm not going to detail the schematic yet as the design isn't 100% complete and it uses modern HCMOS ICs instead of period TTL. Fundamentally it's a FET follower and discrete schmitt trigger front end, a timebase module, some clock, latch and reset logic and a 4 digit counter chain. Utilises only 74HC14, 74HC08, 74HC390, 74HC4060 and 4511 ICs, a J113 follower, 2n2222 based amplifier and schmitt trigger. Sensitivity is 40mV, input capacitance is around 20pF, impedance 1M and its design speed is up to a 20MHz count. This is pretty naff by some standards but there is an accessory connector on the design which allows prescalers to be connected to the front end in Pomona BNC boxes. The first crudely scribbled out one is a 200MHz prescaler.

The whole thing is on cheap stripboard, bar the analogue front end which is dead bug. This is carefully coupled to the main counter chain with some RG174. After the first divider it doesn't matter about the construction.

The timebase and display module along with readout decimal point and frequency scale indicators is complete. The rest is on various breadboards at the moment.

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I'll post back details as I complete bits of it.

29th Dec 2016, 12:43 am	#1
MrBungle Dekatron Join Date: Jun 2016 Location: London, UK. Posts: 3,687	Yet another homebrew frequency counter... Decided contracting everything out to a PIC felt like cheating. Plus I don't enjoy playing with MPLAB's toolchain. Ergo, a 1970's magazine style counter is in development. I'm not going to detail the schematic yet as the design isn't 100% complete and it uses modern HCMOS ICs instead of period TTL. Fundamentally it's a FET follower and discrete schmitt trigger front end, a timebase module, some clock, latch and reset logic and a 4 digit counter chain. Utilises only 74HC14, 74HC08, 74HC390, 74HC4060 and 4511 ICs, a J113 follower, 2n2222 based amplifier and schmitt trigger. Sensitivity is 40mV, input capacitance is around 20pF, impedance 1M and its design speed is up to a 20MHz count. This is pretty naff by some standards but there is an accessory connector on the design which allows prescalers to be connected to the front end in Pomona BNC boxes. The first crudely scribbled out one is a 200MHz prescaler. The whole thing is on cheap stripboard, bar the analogue front end which is dead bug. This is carefully coupled to the main counter chain with some RG174. After the first divider it doesn't matter about the construction. The timebase and display module along with readout decimal point and frequency scale indicators is complete. The rest is on various breadboards at the moment. I'll post back details as I complete bits of it.