Switch on delay timer - Page 1
Forum section: electronics / beginners

author: keef46
author_rank: Contributor
timestamp: March 23, 2021, 03:16:57 pm
content: I am trying to make a simple switch on delay timer.... there are loads of examples around, i found this product though - does what a i want, so i am just hoping to copy the circuit.https://www.aliexpress.com/item/4000320803968.html?spm=a2g0o.detail.1000014.1.13aa4a0exWq69b&gps-id=pcDetailBottomMoreOtherSeller&scm=1007.33416.213724.0&scm_id=1007.33416.213724.0&scm-url=1007.33416.213724.0&pvid=c058b30d-c042-4868-ade0-1d2f4a2ea135&_t=gps-id:pcDetailBottomMoreOtherSeller,scm-url:1007.33416.213724.0,pvid:c058b30d-c042-4868-ade0-1d2f4a2ea135,tpp_buckets:668%230%23131923%2345_668%23888%233325%238_23416%230%23213724%230_23416%234721%2321967%23159_23416%234722%2321972%239_668%232846%238109%231935_668%232717%237563%23548_668%231000022185%231000066058%230_668%233422%2315392%23697_4452%230%23214000%230_4452%233474%2316498%23913_4452%234862%2324463%23900_4452%233098%239599%23116_4452%235108%2323442%23386_4452%233564%2316062%23609The circuit doesn't mention the transistor used - but i think its a J3Y / S8050 (seen this on photo's of other clones of the board...). So made it up quickly on bread board - but it doesn't work? I have used a 47K resistor for R1, after about 4 secs i see pin 3 of the 555 switch to VCC (12V). The LED does not switch ON though - the base of the transistor does switch to 9V??? Any advice as to what's going on appreciated - I'm a novice!

author: cheater
author_rank: Regular Contributor
timestamp: March 23, 2021, 03:34:42 pm
content: It would be super helpful if you posted the schematic that you ended up using, and a photo of the completed circuit.

author: Ian.M
author_rank: Super Contributor
timestamp: March 23, 2021, 03:39:21 pm
content: The base should *NEVER* get to 9V. A NPN transistor has two diode junctions, C-B and B-E. The B-E junction is forward biased when the transistor is on, which typically limits the base voltage to about 0.7V more positive than the emitter (assuming the base is fed through a resistor).==> Either you've got the transistor pinout wrong, or its emitter isn't connected to Gnd.@Cheater: +1 for photo, but the schematic is at the link Keef gave.

author: keef46
author_rank: Contributor
timestamp: March 23, 2021, 03:54:01 pm
content: The schematic is in the link.... but just to make life easier....It does seem like something really wrong, like I have got the pinouts or connections wrong... i have double checked, but i will triple check....

author: Ian.M
author_rank: Super Contributor
timestamp: March 23, 2021, 04:07:38 pm
content: Post a photo. There are many traps for 'young players' when breadboarding on solderless breadboards, and the easiest way to see which one you've fallen into is to see it!. Make sure its a well lit, in focus closeup as we need a good enough picture to read IC and other component markings.

author: keef46
author_rank: Contributor
timestamp: March 23, 2021, 04:08:13 pm
content: Photo's.... cant find anything wrong???

author: Ian.M
author_rank: Super Contributor
timestamp: March 23, 2021, 05:00:39 pm
content: Cheap 'duPont' pin to pin jumpers on a single breadboad should be banned!See my comments here:https://www.eevblog.com/forum/beginners/powering-large-breadboard-setup/msg1120261/#msg1120261and here:https://www.eevblog.com/forum/beginners/standard-breadboards-and-wire-size/msg1326025/#msg1326025You'll avoid a lot of trouble if you use 24AWG solid core wire for breadboard jumpers, individually cut to length, and ends stripped and formed to fit. Scrap Cat 5 (+) Ethernet cable is a good source of free jumper wire. Don't use Ethernet patchcord cable - its stranded and will FUBAR your breadboard.Start by checking (with power off) continuity using your DMM, from the emitter leg to the Gnd pin of the 555. If they aren't connected, pull out that blue jumper, and check it for continuity!We need either a closeup of the transistor good enough to read the markings, or its exact markings typed out so we can find its datasheet and verify the pinout.

author: WattsThat
author_rank: Frequent Contributor
timestamp: March 23, 2021, 05:36:51 pm
content: If the 555 pin 3 goes high after 4 seconds, the left half of the circuit is okay.Lift the end of the 1K resistor going to the base of the S8050 and connect it to ground.If the LED does not light when it goes through the the 1K to ground, troubleshoot that. Either the LED is bad/open, the resistor is perhaps more than 1k or its not grounded. Work it out.Take a new 1k resistor, connect one end to the transistor base and the other end to 12V. You should hear the relay click on. If not, go looking. Check the transistor. The relay. The wiring.Troubleshooting is just testing one thing at a time. Find where the voltage disappears or the current doesn’t flow. Just about ever attribute of a component can be checked, somehow. Multimeters check voltages, currents, measure resistors, capacitors, diodes, transistor, etc. It’s just a just a game of finding the wrong something. It’s up to you to understand how the circuit should work so you can verify how it does or doesn’t work.

author: keef46
author_rank: Contributor
timestamp: March 23, 2021, 07:17:46 pm
content: Quote from: WattsThat on March 23, 2021, 05:36:51 pmPerfect - thanks! Duff Transistor (or i damaged it....). All working now.

author: Terry Bites
author_rank: Super Contributor
timestamp: March 24, 2021, 05:28:27 pm
content: Don't put the LED in series with the base. It only indicates current is flowing into the base and not into the load. Just cough up the for the extra resistor. Put it and the LED across the relay.That said, it will work fine. Use a 7555 and reduce C by a factor of 10 and up the resistor by a factor of 10. The timing will be more predictable. Use a tantalum cap.