Delay, then hold on, power up timer circuit needed please. - Page 1
Forum section: electronics / beginners

author: Chris Wilson
author_rank: Super Contributor
timestamp: April 30, 2021, 01:18:52 pm
content: I have two generic Chinese timer relay boards, but neither seems able to do what I need. That is:When 12V DC is applied to my box of tricks a 12V DC supplied GPS locked oscillator circuit (Leo Bodnar) starts up immediately. After say 20 seconds to establish a GPS lock has occurred the timer circuit closes a normally open relay sending the same 12V DC source to "other devices" until such a time as all 12V DC is removed. On the next power up it does the same again,Timing can be fixed, or a modest amount up (longer time period) might just be useful.The device I have has a relay with one moving contact that's normally closed. On powering up the timer module the NO contact closes for the duration set, then opens again when the timed period ends. This does not achieve what I am looking for. Maybe I could use this module still with some semiconductor device to do the switching, or switch and hold a second relay? I need to control about 5 Amps max @ 12v DCMany thanks. The Chinese modules on Ebay have scant details or instructions, it may be easier to adapt what I have or make my own.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 30, 2021, 01:38:45 pm
content: I want to make sure what you want. You want to power the GPS first and then after a time delay power other circuits. The power stays on until you turn it off manually right?

author: Chris Wilson
author_rank: Super Contributor
timestamp: April 30, 2021, 02:25:27 pm
content: Quote from: BeBuLamar on April 30, 2021, 01:38:45 pmThat's it exactly, GPS first, then the rest, then they ALL stay on until I kill the primary power source. Done as simply as possible please, thank you.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 30, 2021, 02:46:03 pm
content: OK so the whole thing is powered with 12VDC so whatever delay relay is it must run on 12VDC right? Now I need to know your budget. Also if you can tell me what you have. Possible what you already have can be changed to do what you want. I have several of them but what I have only work on 24VDC or 120VAC. The prices of the ones I have are about $50 to $100.

author: Chris Wilson
author_rank: Super Contributor
timestamp: April 30, 2021, 02:56:00 pm
content: Well, that's a bit more than I hoped to spend to be honest, I am sure some of the Chinese Ebay things will do what I need, it's identifying them and the hassle of waiting and wondering if the purchase will actually do the desired task. I can achieve what I need manually in the short term, but it definitely needs automating long term. Changing what I have sounds intriguing... Thanks

author: ledtester
author_rank: Super Contributor
timestamp: April 30, 2021, 03:06:07 pm
content: Here's how to do it with an Arduino + a relay module:https://www.seeedstudio.com/blog/2020/01/03/arduino-tutorial-control-high-voltage-devices-with-relay-modules/The program (at the end) is very simple. You could even get fancy and have the Arduino monitor the GPS PPS output to make sure it has acquired a lock before activating the relay.Look on aliexpress for cheap Arduinos (like a Nano) and relay modules.

author: RichC
author_rank: Contributor
timestamp: April 30, 2021, 03:08:32 pm
content: An RC circuit + comparator and a mosfet would do the job I would think? Then you could drop the relay entirely (unless you particularly want it).This circuit seems to work in sim, componenets are fairly arbitrarily selected, so use whatever is available and fits the power / voltage requirements.Results, timing can be tweaked with R1 and C1.