1 Hz crystal clock signal not 1 Hz - Page 1
Forum section: electronics / beginners

author: buck converter
author_rank: Regular Contributor
timestamp: July 27, 2017, 09:12:09 pm
content: My friend and I built this circuit and it was spot on 1 Hz, measured by our multimeter. 1 day later without moving a wire, it is now closer to 0.6 Hzhttp://www.hackersbench.com/Projects/1Hz/When we replaced the crystal, it did not fix anything. This is the crystal we used:https://www.digikey.com/product-detail/en/abracon-llc/AB38T-32.768KHZ/535-9034-ND/675229.

author: bson
author_rank: Unknown
timestamp: July 27, 2017, 09:19:54 pm
content: You missed connecting a bunch of pins on the counter to ground. Floating CMOS gates will collect charge.

author: pigrew
author_rank: Frequent Contributor
timestamp: July 27, 2017, 09:21:12 pm
content: The first thing I'd do is as decoupling capacitors to your ICs. Add around 0.1uF from the vdd pin to ground on each IC. It probably won't make it work, but it's a good idea to do.

author: MK14
author_rank: Super Contributor
timestamp: July 27, 2017, 09:22:11 pm
content: The second IC (on the right), seems to be missing a power pin connection. Since there are no visible wires on one entire side of it.Maybe your Cat/Pet got hungry during the night ...

author: rdl
author_rank: Super Contributor
timestamp: July 28, 2017, 12:18:32 am
content: The web page where you got the circuit has a layout already done that you can duplicate exactly on your bread board. Try changing your circuit to match that layout and see how it works.(1Hz Time Base Layout, Standard Radio Shack style protoboard.)

author: buck converter
author_rank: Regular Contributor
timestamp: July 28, 2017, 01:58:22 am
content: Tracked the problem down to the 32.7680 KHz crystal, which is oscillating at 4 KHz. Is this waveform normal? picture athttp://imgur.com/a/vsqO4

author: Audioguru
author_rank: Super Contributor
timestamp: July 28, 2017, 02:15:20 am
content: The datasheet for the crystal shows 12.5pF load capacitance but your circuit has 30pF plus all the capacitance between the connector strips of the breadboard. Use 12pF capacitors and get rid of the breadboard and use a properly designed pcb instead.

author: lowimpedance
author_rank: Super Contributor
timestamp: July 28, 2017, 02:15:40 am
content: Quote from: rdl on July 28, 2017, 12:18:32 amExactly this, then report back if it still doesn't work.As it stands by the photo its never going to work.

author: rdl
author_rank: Super Contributor
timestamp: July 28, 2017, 08:05:58 am
content: At one time, I built a 1 Hz generator using a CD4521B and a 4.194304 MHz crystal on a plastic breadboard and it worked fine. It was used to set the gate time of a frequency counter and I think I may still have that project somewhere in a box.

author: nali
author_rank: Frequent Contributor
timestamp: July 28, 2017, 08:29:46 am
content: Looks like pins 10 & 11 are transposed...

author: Gyro
author_rank: Super Contributor
timestamp: July 28, 2017, 08:36:12 am
content: Quote from: rdl on July 28, 2017, 08:05:58 amIronically (for a breadboard) it was actually the high crystal frequency that saved you. They run at much higher drive level and load capacitance than a whimpy little 32kHz crystal can tolerate.