In the attached circuit, I am attempting to use a 555 timer to turn a solenoid off for a set amount of time on a button press. When powered on, the solenoid turns on. When the button is pressed, the solenoid turns off. The problem is that the solenoid will turn off for about a second and turn back on. I've adjusted the R1 and C1 values for timers of 11 seconds and 4 minutes with no noticeable difference. The solenoid is 12V and 1.4 amps (manufacturer specs).

I also set up the circuit to turn on the solenoid upon button press for a set amount of time. This worked successfully, so I know the parts are good.

Any suggestions?

 

The transistor shorts out the power supply when it is turned on. You need to use a circuit something like this:

 

Welcome to AAC!

The datasheet should say that trigger must return to a voltage above 1/3Vcc before the timer times out. You can't connect it to ground.

You have the solenoid coil connected wrong. As wired, it will turn off the solenoid when the timer output is HIGH. Before and after that, the solenoid will be energized.

You should have a current limiting resistor on the base of the power transistor.

What is the coil resistance?

 

Yeah, I've seen diagrams like that, but I had a Darlington npn transistor and not a pnp one.

I thought the base of the transistor could handle whatever the 555 outputted so I resistor at the base wouldn't be necessary. My multimeter is busted, so I do not know the coil resistance.

 

Yeah, I've seen diagrams like that, but I had a Darlington npn transistor and not a pnp one.

I thought the base of the transistor could handle whatever the 555 outputted so I resistor at the base wouldn't be necessary. My multimeter is busted, so I do not know the coil resistance.

Disconnect the relay and diode. Reconnect the relay so its coil is in series with the collector of the NPN transistor. Then reconnect the diode in parallel with the relay coil.

 

Disconnect the relay and diode. Reconnect the relay so its coil is in series with the collector of the NPN transistor. Then reconnect the diode in parallel with the relay coil.

While the timer is active, the solenoid should be off. Your suggestion would work the wrong way round.

 

You have the solenoid coil connected wrong. As wired, it will turn off the solenoid when the timer output is HIGH. Before and after that, the solenoid will be energized.

That is the way TS wants it to work.

 

Didn't notice earlier that the transistor shorts the battery.

 

The datasheet should say that trigger must return to a voltage above 1/3Vcc before the timer times out. You can't connect it to ground.

You have the solenoid coil connected wrong. As wired, it will turn off the solenoid when the timer output is HIGH. Before and after that, the solenoid will be energized.

I see what you mean about the trigger connected to ground. I drew that incorrectly, the switch is between the resistor and pin 2, not pin 2 and ground.

And that's how I want the solenoid to behave, energized when the timer output is high. But the timer output is only staying high for a moment. Or so I think, guess I should replace my multimeter.

 

And that's how I want the solenoid to behave, energized when the timer output is high.

That's the opposite of what you said in your original post.

 

I drew that incorrectly, the switch is between the resistor and pin 2, not pin 2 and ground.

If you drew the rest of the circuit correctly, the transistor is shorting the battery.

 

That's the opposite of what you said in your original post.

You're right. Sorry I worded my reply poorly and wrong. Solenoid off while the timer output is high.

 

Yeah, I've seen diagrams like that, but I had a Darlington npn transistor and not a pnp one.

If you have another NPN transistor you could use something like this:

 

If you have another NPN transistor you could use something like this:

I was planning on using a relay if I couldn't figure this out. And I was just going to connect the relay to the collector of a transistor connected to the timer. Would that second transistor really be necessary?

EDIT: Found the link with that image, I see why it has 2 transistors.

 

While the timer is active, the solenoid should be off. Your suggestion would work the wrong way round.

oops....I misread the TS post.

 

I was planning on using a relay if I couldn't figure this out. And I was just going to connect the relay to the collector of a transistor connected to the timer. Would that second transistor really be necessary?

EDIT: Found the link with that image, I see why it has 2 transistors.

If you are using the non-CMOS version of the '555 (NE555) then the chip will drive a relay coil directly - no transistor needed. The NE555 will sink up to 200mA. Simply connect the relay coil between the '555 output and the supply and the relay will be on except during the timer period.

 

Post # 1, solenoid, 12 V @ 1.4 A.