Instructables

Can I use a 555 timer to cycle on 1 minute and off 1 minute?

I am kinda familiar with the 555 timer for flashing lights and such, but I am in need of a circuit which will cycle on for 1 min and off for 1 min. Can this device (555 timer) be used for such low frequencies. It will ultimately control a 12v relay to run a bilge pump in an Instructables evaporative cooler which I am making (this mod is my idea which I will share with the original inventor if it works). I guess that if the low frequency is possible I will also need a power transistor to step up to the voltage/current needed to operate the relay. Any help greatly appreciated........ Thanks, Peter :-)

iceng1 year ago
What is more important, the 50% on 50% off cycling
or the 1.0 minute repeating period over temperature and time ??
ppowell14 (author)  iceng1 year ago
Haven't really decided yet as I need to experiment to establish the most efficient cycle for maximum cooling efficiency. At a guess I'd say the 50% on 50% off. I am currently still building the cooler and have just finished the plumbing part but I wanted to get some ideas for the electrical control ahead of time.
OK here is a 50/50 guaranteed.
You may need to play with the RC for 1Hz
I just guessed at it.

PS polycarbonate capacitors are the stable ones compared to
Tantalum or Electrolytic capacitors.
and Vishay makes stable resistors.

A

5050.gif
ppowell14 (author)  iceng1 year ago
Okay, it's me again the Swamp Cooler Guy :-).... The beast is up and running though just in manual mode right now (cools 90 F to 72 F). I did some experimentation and my original estimate of 1 min on/ I min off is not supported by the data I collected. The optimum cooling cycle seems to be 1 min on/ 4 min off for the pump. This is very good for battery life as the pump uses 3A whereas the fan (on all the time) uses 1.2A. I bought all of the components for your circuit design so can I trouble you to help me get the 1:4 cycle from this circuit. Thanks in advance,
Peter
Sure, here it is with only one wire change !
ppowell14 (author)  iceng1 year ago
Hi again, got the circuit bread boarded and working but the cycle is 1 sec on to 4 secs off. Will changing the cap to 330uf and the 100K resistor to 470k give me 1 min/4min cycle? I'm assuming that the 470 ohm resistor is just to protect the transistor and doesn't affect the on/off cycle.
Thanks, Peter
  • Use this CIRCUIT version for the 1min time
  • R1=10 K
  • R2=2.2 M = 2200 K
  • C1=330 uF
  • Used Bowden's site for the math

ppowell14 (author)  iceng1 year ago
Thanks! ..... This will be So Cool .... literally :-)
ppowell14 (author)  iceng1 year ago
Wow! Thank you so much. This is the first time I have asked a question on Instructables........ always a bit intimidated as electronics are not my strong suit, but thanks to all for boosting my confidence :-). You guys are so nice!
lukerobs9 months ago

looks like your doing what i need, i intend on using mine for aeroponic irrigation, although some have posted good info on here nobody seems to have an answer hmm... How about adjustable resistors defo go with 7555

ppowell14 (author)  lukerobs9 months ago

Hi, I finally got mine to pulse on for 1 min and off for 4 mins though not exactly. The times tend to vary a bit each time I switch it on but it's fine for my intended use. I am currently overseas on a job so I don't have my notes with me but if you can wait until after Feb 18th I will be back. I also made a printed circuit board of which I can give you the plan. BTW the resistor/Capacitor values suggested in the thread above do not give the required values, I had to do much experimenting to get the 1/4 min ratio. You could try adjustable resistors but the Cap value seems to be the key. I used 300uF (2 caps in parallel to get this value)

Can you take a picture when you get a chance too, ive been looking for weeks for a timer that could do this, i could only find expensive £200-300 ones which i was never going to buy, cool looking forward to feb 18th now

ppowell14 (author)  lukerobs7 months ago

Hi, I'm back from my travels and have some pics and schematics. I'll try to post them above. they are 12 meg so don't know if it will work. If not I will give you a link to my file storage.

ppowell14 (author)  lukerobs8 months ago

Hi, Sure I can take a pic plus I have the circuit board print which can be transferred to a copper covered board blank. Total cost was under $20.00 which included all my screw-ups :-) .

Will be in-touch,

Peter

ppowell14 (author) 7 months ago

File showing the final circuit both in perf board and pcb.

AndyGadget1 year ago
Yes, but it would be best to use the CMOS version of the 555 - the 7555 which gives better timing accuracy over long periods.  Also use a polyester film capacitor as the timing change with varying temperature will be less.  The 7555 can source 100mA directly so if you're using a low current relay you could leave out the transistor. 

Use an online calculator to choose the resistor values, (they will be in the order of 10uF and several megohms) and I suggest you use a 1M pot in series with the resistor to fine-tune the timing and compensate for component tolerances.
ppowell14 (author)  AndyGadget1 year ago
Thanks! I never knew about the 7555. Can't wait to get started :-)
rickharris1 year ago
Yes BUT not very accurately
That is a nice calculator it gives standard component values.
Yes it's doable. Google for a 555 timer calc and you'll find a helpful site that gives you the base schematic then asks how often you want the timer to fire and then fills in the resistor and capacitor values needed to achieve that cycle.

http://houseofjeff.com/555-timer-oscillator-frequency-calculator/

I think it would be better if you used a micro controller. Then you have more freedom as to what cycle you want the pump to run on. So if the pump needs to kick in every 5 minutes or more you can just change the code a bit to make that happen. Rather than having to change out a bunch of components. 
ppowell14 (author)  mpilchfamily1 year ago
Thanks for the link to the calculator. I think the micro controller is a bit beyond my capabilities so I will start with the 555.