You could give the following circuit a whirl.Īt power-up and at rest the reset pin (pin 4) is pulled low by R3 keeping the output (pin 3) low. Probably not good design practice to switch the 555's supply voltage, it'll probably give the poor little thing a headache! The one question I had is regarding the flyback diode that suggested - is the diode D1 in the correct position and orientation for this? What does this actually do? Does it protect my 555 in this case from getting increased voltage on the output pin when the relay is shut I still want to use the relay here in addition to the 555 because the DC motor pulls a higher current from the stop-to-start and I wasn't sure the 555 could handle something that might be a very brief 4-6A draw - so I figured using the 555 to trigger the relay might be the safer way to go? This seems to work practically, but if there is any feedback on this I'm of course open to hearing. I can of course change the time before shutdown by increasing R1 to create a longer delay before it shuts down. The below seems to work, where closing the switch turns on the relay (closing the relay switch and powering the load - a motor in this diagram), then it turns off after a short time. Thank you everyone for the informative replies! After reading, I decided to try this using a 555 IC instead of just the R-C circuit to trigger the relay. Simulate this circuit – Schematic created using CircuitLab Is my problem that the R2 resistance is dropping the voltage too much before it even hits the capacitor and relay? I used a multimeter to measure voltage drops across R2, RLY, and C1 and the C1/RLY only seem to use 0.8V or so which explains partially why the RLY isn't turning on. 001 * 1000 = 1, but using the setup below, the relay never engages. I thought the RC time constant would be 1 sec since C1*R2 =. I have D2 connected to the RLY's "normally closed" output, so when I turn on the switch, D2 also turns on, but it never turns off like I want it to. Power source = 12VDC laptop-style power brick, which actually supplies closer to 12.5VDC, rated 8A. If I'm reading the datasheet correctly, it seems this is a 12VDC relay, but the coil activates around 9VDC? So if switch is closed for 3 seconds, this LED should only be on for the first 1 second. This is working as expected right now.ĭ2 = the LED I want to turn on immediately when switch is closed, but I want it to turn off after 1 second if the switch is kept closed. This should be on when switch closed, off when switch open. Below is a diagram of what I've attempted but it doesn't work and I'm not sure what I need to do to fix it.ĭ1 = an indicator LED just to let me know the switch works. I'm trying to design a circuit that uses a momentary switch/push button to turn on an LED, then it turns off after 1 sec if the switch is held in the ON position longer than that.
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