Electronic – an efficient way to divide clock by 1000 or more


Context: This is a home brew project that incorporates NO microcontrollers as a learning exercise. I need to time something up to 20 seconds long, down to the nearest 100th of a second, and display the time interval measured. I'm using a 4 digit 7 segment common cathode led for the display.

I have a 100khz crystal and I want to display the tens, ones, tenths, and one hundredths of seconds (ie 23.36 seconds) on a 4 digit 7 segment led display. I thought I could use the 4026 chip, a decimal counter and led driver. However I have to chain 3 of them just to get to 100hz, then chain another 4 of them to get the 4 digits of display. 7 ICs (plus multiplexing logic because the display uses common abcdefg leads, plus resetting etc) seems like a LOT.

Am I missing a much simpler way to approach this? The 'rules' are: any ICs or other components but no software (no MCUs).

Thank you.

Best Answer

Keep it simple. You can find ICs that will divide the 100 kHz by 1000, like the 74HC4059 programmable divide-by-N counter, but most of these will cost you an arm and a leg, where a couple of cheap 74HC390 counters will do. The HC390 is a dual BCD counter, so for the second you only need half of the IC, but it's cheaper than a single BCD counter.