Single push button set/reset with turn off delay - Page 1
Forum section: electronics / projects

author: reyntjensm
author_rank: Regular Contributor
timestamp: September 20, 2022, 09:04:35 pm
content: I want to build a very simple set/reset circuit with off delay functionality. I want to set and reset the circuit with a single push button. I started with two 555 timers. One is used as a set/reset and controls the power to a second 555 used as an off delay. When the circuit is set and the timer turns off nothing happens when i push the button as this will only reset the first 555. I don't like this, the circuit should turn on again. I can't find an easy solution to solve this issue.I've attached my schematics from LTspice.The delay should be around 10 hours, i know the 555 is not the best solution for this but the exact timing doesn't really matter for this application.After a while struggling with this i had enough. I had the idea to use an Attiny85 for this but it looks like it's impossible to buy a few Attiny85's. Any suggestion about an alternative micro?

author: james_s
author_rank: Super Contributor
timestamp: September 20, 2022, 09:30:46 pm
content: Recently someone was asking for a 10 minute delay with a 555 which is unreasonably long and now you're asking for 10 HOURS. This really is not the correct part for the job, unless you want to use it as a clock source for a binary counter. A 50 cent microcontroller would make this project trivial with the only external component being a single decoupling capacitor.

author: Benta
author_rank: Super Contributor
timestamp: September 20, 2022, 09:31:48 pm
content: The MC14541/CD4541 will do what you want, but for 10 hours you'll need a 1.1 Hz clock. A 7555 perhaps?

author: reyntjensm
author_rank: Regular Contributor
timestamp: September 20, 2022, 09:36:28 pm
content: Quote from: james_s on September 20, 2022, 09:30:46 pmcorrect, it took me some time to realize that.

author: Zero999
author_rank: Super Contributor
timestamp: September 20, 2022, 09:40:39 pm
content: Here's a circuit I made using a couple of transistors. It'll work for delays of up to 10 minutes with poor accuracy, but not 10 hours.https://www.eevblog.com/forum/projects/onoff-switch-with-timer/Use a microcontroller.

author: Benta
author_rank: Super Contributor
timestamp: September 20, 2022, 10:14:09 pm
content: Quote from: Zero999 on September 20, 2022, 09:40:39 pmThen why post it?

author: mc172
author_rank: Frequent Contributor
timestamp: September 20, 2022, 10:49:07 pm
content: Q2 is backwards.

author: ledtester
author_rank: Super Contributor
timestamp: September 20, 2022, 11:11:44 pm
content: Quote from: reyntjensm on September 20, 2022, 09:04:35 pmUK Farnell has the attiny45 in stock:https://uk.farnell.com/microchip/attiny45-20pu/mcu-8bit-attiny-20mhz-dip-8/dp/1288352?st=attinyFor cheaper alternatives, look on this page, e.g. attiny414, attiny20.https://uk.farnell.com/search/prl/results?range=inc-in-stock&st=attiny&sort=P_PRICEThe newer attiny's are programmed via a UDPI interface but it is easy to make one with an Arduino, e.g.:https://create.arduino.cc/projecthub/john-bradnam/create-your-own-updi-programmer-1e55f1

author: Chriss
author_rank: Frequent Contributor
timestamp: September 20, 2022, 11:34:04 pm
content: How about Attiny13?Super cheap, available and easy solution.

author: james_s
author_rank: Super Contributor
timestamp: September 21, 2022, 12:53:46 am
content: ATTINY10-TS8R is even cheaper, Digikey has them in stock, 47 cents each in singles. It's a tiny SOT23-6 package.