Will a 555 timer switch on and off, on and off, etc?

[pityocamptes]

I have a small air pump that needs to cycle, the pump draws very little current and voltage ~3.5 volts. Its a mini pump. The specs say 7 seconds on and 7 seconds off for duty cycle. Will a 555 timer circuit do this? 7 secs on and 7 off, 7 on and 7 off, etc until the unit is powered off via a control switch? Anyone have a schematic that I can reference? Thanks!

 

[wingnut]

It can do what you require. See....
http://talkingelectronics.com/projects/50 - 555 Circuits/50 - 555 Circuits.html

 

[pityocamptes]

It can do what you require. See....
http://talkingelectronics.com/projects/50 - 555 Circuits/50 - 555 Circuits.html

Thanks!

 

[CocaCola]

This will get you close...

 

[pityocamptes]

Hey thanks! Since my voltage supply for my timer is going to run off the same supply for the pump (~3 to ~3.2 volts dc at <150ma), will the 555 actually go that low for Vin? Or should I be looking at something like this:

http://www.intersil.com/en/products...e-base-ics/counter-time-base-ics/ICM7555.html

...and if so, is it the same schematic as above? Thanks!

 

[pityocamptes]

Hey were did you get that calculator? I may need to play around with the time frames a little. Thanks!

 

[CocaCola]

Yes, use a 555 rated for your voltage levels... Same schematic...

http://freespace.virgin.net/matt.waite/resource/handy/pinouts/555/

 

[pityocamptes]

Yes, use a 555 rated for your voltage levels... Same schematic...

http://freespace.virgin.net/matt.waite/resource/handy/pinouts/555/

Do you have a list of 555's with different voltage levels? I didn't realize that made different ones. I probably need a low voltage input 555 that has an output of at least 150ma. Thanks!

 

[CocaCola]

Do you have a list of 555's with different voltage levels? I didn't realize that made different ones. I probably need a low voltage input 555 that has an output of at least 150ma. Thanks!

Go to a supplier like digikey or mouser and start looking at the specs... If you need a higher drive current you can add a transistor... Also don't forget to add a flyback diode across the pump... Google transistor as switch and flyback diode for more info...

 

[pityocamptes]

Go to a supplier like digikey or mouser and start looking at the specs... If you need a higher drive current you can add a transistor... Also don't forget to add a flyback diode across the pump... Google transistor as switch and flyback diode for more info...

Thanks. You wouldn't happen to have a schematic that uses a transistor switch in the 555 timer circuit, so that I can get a visual idea? Thanks again!

 

[CocaCola]

Thanks. You wouldn't happen to have a schematic that uses a transistor switch in the 555 timer circuit, so that I can get a visual idea? Thanks again!

I could but you have already been given the path to solving this, time for you to do a little of your own legwork...

Google transistor as switch and flyback diode for more info...

or read the entire document wingnut linked you to...

 

[pityocamptes]

No problem. So would a circuit like this work, with the pump being in the same spot as the LED? Let me know. Thanks!

http://www.allaboutcircuits.com/vol_6/chpt_8/8.html

 

[pityocamptes]

Here is a schematic using switches and diodes, I added the diodes, "M" is the motor of the pump, did I do the diodes right? Does the schematic look right? Thanks!

 

[(*steve*)]

The diode in series with the motor is not required.

The other diode is in the incorrect place. It should be across the motor.

3V may be insufficient to power the 555.

You may have to decouple the 555's power from the motor

The motor (with these modifications) will see just under 3V.

What is R4 for? It's not needed, remove it.

 

[pityocamptes]

Thanks. How does this look?

 

[CocaCola]

I believe you have addressed most issues from a quick look over, just make sure the 555 you get will operate at 3V and also as Steve touched upon the motor might make a bit too much noise for the 555 to be happy... Make sure that C2 is as close to pin 8 as possible, you can bridge directly from pin 8 to pin 1 of the 555 with C2 making the distance minimal... You might also need a few other value caps to help with the noise as well but that will have to be determined at that time if you have issues...

 

[pityocamptes]

I believe you have addressed most issues from a quick look over, just make sure the 555 you get will operate at 3V and also as Steve touched upon the motor might make a bit too much noise for the 555 to be happy... Make sure that C2 is as close to pin 8 as possible, you can bridge directly from pin 8 to pin 1 of the 555 with C2 making the distance minimal... You might also need a few other value caps to help with the noise as well but that will have to be determined at that time if you have issues...

How will I know if I have noise? Will the "noise" provide a false trigger? If I do get noise, where do I place the caps? For my programmed time I was going to use:

R1 = 600k
R2 = 500k
C = 20uf

I may change them slightly, but this is what I was looking at... thoughts? Thanks!

 

[pityocamptes]

Oh, also is the schottky diode, 1n5817 facing the correct way?

 

[CocaCola]

Yes, the diode is shown correct...

 

[(*steve*)]

How will I know if I have noise?

Weird stuff will happen.

It's hard to be more specific, but yeah, look out for odd things when the motor is running and also when it switches off.