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#363 binco

BINCO is a little up or down "fidget" counter, Project #19 of the Boldport Club.


▶️ return to the LEAP Catalog


The BINCO a binary counter that can be configured to count up or down. It uses Snaptron domes as buttons (on, slow/fast and reset). The heart of the counter is a 555 timer driving a 74HC4020D 14-bit Binary Counter from which 11 taps drive some nice reverse-mount LEDs.

Parts and Unboxing


1x 14-bit binary counter IC, Nexperia 74HC4020D,652
1x 555 timer IC, TI TLC555QDRG4
11x Reverse mount green SMD LEDz, Kingbright KPTL-3216CGCK
1x N-channel MOSFET SMD transistor, ON Semi BSS123
16x 1.5KΩ 0805 resistors, Multicomp MCWR08X1501FTL
2x 47KΩ 0805 resistors, Multicomp MCWR08X4702FTL
2x 1µF 0805 capacitors, Multicomp MC0805F105Z160CT
1x CR2032 battery clip, Multicomp BC-2001
1x Dome (reset), Snaptron GX05300
1x Double action dome (count slow/fast), Snaptron DT10340N
1x Dome (on/off), Snaptron F10450
1x PCB
1x Piece of adhesive sheet

kit_parts kit_pcb_front kit_pcb_rear

How It Works

The 555 timer is in an astable configuration, initially disabled.

  • when "count slow" button is pressed, ti runs at around 15 Hz
  • when "count fast" button is pressed, it runs at around 320 Hz

The timer provides the clock pulse to the 74HC4020D 14-bit Binary Counter. The 74HC4020D provides 12 taps of a ripple-carry chain, but the first (pin 9) is not used, probably because the chip doesn't provide pins for the next two stages.

As always, Boldport provides a very nice infographic for the project, but here is my re-drawing of the circuit (it's how I make sure I understand what is going on!)



  • the "on" switch only affects the LEDs; the ICs remain powered by the battery at all times. I suspect a sneaky trick to always "remember" the last state!
  • but R100 stops the 555 timer running while not "on" by pulling down the reset pin.


I decided to build the "count down" configuration, which involves making sure the LEDs point to the edge of the board, and bridging the down/right count pad.

In this configuration, R101 and IC10 are optional, so I left them off the board.




Here's a quick demo, "fast mode".


Credits and References