DIY Aeroponic Timer - 555 circuit


Hi all.

This has been my project for the last few days, and I’ve finally cracked it, so I’m happy to share it with you. Aeroponic timers are expensive, but relitavely simple and cheap devices to the amateur electronics geek. This adjustable timer turns a pump ON for 7-27 seconds, and OFF for 20seconds – 4 minutes. The times could be easily changed longer or shorter by using different value potentiometers. The components cost me under £15 but I did buy a 12v transformer as well. You don’t have to use 12v DC for the circuitry, you could use a 9v battery with different components. However I opted for mains power because I didn’t want batteries running out on me. I haven’t touched any electronics for over 10 years when I did my apprenticeship in manufacturing engineering, but I managed - so it’s not rocket science.

DISCLAIMER – The following timer is a device that uses mains voltage. Although safe to use, in replicating this device, any mistakes in wiring could lead to electric shock with mains power. This guide is for information only. The following timer could be made to work with a safer 12v DC water pump, but would require different components from the ones specified. (just don’t do it if you don’t know what you’re doing, stoned or drunk. Check all circuitry using multimeters or LED’s before attaching mains power!)

What we’re making is a Timer circuit that controls a relay switch that switches a water pump ON and OFF to an adjustable timeframe.


555 Timer chip + mount
Potentiometer 1M ohm
Potentiometer 100k ohm
Resistor 33k ohm
Capacitor 330uF
Silicon Diode 1amp
Solid State Relay 12v / 240v (or 110v)
12v DC transformer
Circuit Board

I also used a double plug socket, so that I can use 2 pumps on the same timer. I also used a “bread board” type circuit board to test the circuit before soldering. I also used an LED to make sure the circuit was working. ( I would rather use an LED instead of a relay to make sure everything is working, I only connected the relay and mains power when I was 100% sure the circuit was working. Using a multimeter to check as well.

Assemble components on a “bread board” type circuit board (see photo). In the final build when the timer is ON there will be 10v between pin 3 and pin 4 of the chip. This is where we will connect the coil of the relay. (A relay is an electronic switch, when a small current is passed through it will switch a higher voltage switch) In order to check the circuit, use an LED between pin 3 and -12v terminal. (make sure LED and Diode are the correct way round, this had me stumped for ages). If the circuit is good, the LED should be ON for a long time and OFF for a short time.

Check relay switch with a multimeter or circuit tester. Find out which way the switch goes when a 12v current is passed through it. For this build, we need the relay to turn OFF when a current is present. THE RELAY CONTROLS MAINS VOLTAGE!! Personally I prefer to not have the relay connected to the circuit board, it’s just asking for trouble. I connect the small 12v wires to one side of the relay, and the thicker mains wires to the other side. I then tape it up good and proper with electrical tape so that the Mains pins are never going to touch any of the small circuitry or the box edges, my hands etc. (see photo of taped up relay)

Once happy that everything is working and safe, solder onto circuit board and trim the board to fit in the box. I prefer to tape any exposed wires with tape, so as to not short circuit anything when box is assembled.

Drill holes in the box for the potentiometers (pots) and wires, solder pots onto circuit. Again, because circuit has been re-built, I will check the circuit works by checking the current at the relay switch with a multimeter. Only once I am satisfied with this will I plug in the mains. Assemble everything in the box, check again.

There you have it! To further improve the timer, I added a photoresistor in series to the pot controlling the OFF time. This pushed the OFF time up to 7-8 mins when it’s dark, instead of 4 mins in light. Also, you could add a thermistor to the ON pot, to lengthen the ON time when it is hotter and your plants need more water.


I'm not a master of electronics, so please don't ask complicated questions. I came up with timings through trial and error with different value resistors. Hope you manage to make something similar! and stay safe!!


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Active Member
Well done sir !
The 555, well that takes me back to making my own circuits with them waaay back
in the 80's.....OMG i'm old...

Just wanted to say well worked out ! Using a 555 - spot on, those little buggers will run for donkeys years and are quite forgiving if you are a Volt or two out, i'd almost
forgotten about them it's been that long since I used one.
Sounds like you don't need any help there, guesstimating components too, awesome
stuff....A man after my own way of engineering !
You got it sorted out already, but thought i'd just let you know that if you do get stuck with anything i'm certain I have a couple of old books (Radio Shack) one on different 555 556 circuits and the other is like a glorified data sheet on 555's and dual ones, pin outs etc etc etc....Probably has some voltages etc too.

So if you do get stuck pm me and i'll go hunting for them.....

At the moment i'm a bit fresh to Hydroponics but the methods i've seen used so far look quite simple to mould into a DIY project.
I've seen the fill/drain method, very simple, also seen a spray nozzle type set-up but guess you are having to de-clog nozzles, prime pumps etc etc.....So the one that caught my eye as simplest to design and create was the fogger/mist type ones.

I've never used one of those devices, but they seem cheap enough and new ceramics can be purchased to repair ones that are worn, so i'm thinking of that method....

At risk of starting a Hydro-method war - Just wanted to ask if anyone has had any experience of the fogger type, is it better/worse than fill/drain, any problems etc ?
It certainly 'sounds' a good method of getting both nutes and O2 to roots, but i'm a noob so maybe those foggers are only good for extremely tacky plastic ornaments...

Any info would be helpful....

Also have been trying to source the LED's used in the top of the range LED grow panels with a view to making my own for much less...
LED panels seems a great idea, i'm just a bit sceptical as I am with anything new, but the intensity of LED's is on the increase all the time and cost of producing them should come down as they sell more, so i'm hoping they will become increasingly viable.

Any one else interested in looking into these methods, or any one have better ideas and ways then plz PM me or let me know somehow and we can team up if you wish.


Well-Known Member
The only problem I see is "For this build, we need the relay to turn OFF when a current is present." That means you have a SS relay that is a NC - normally closed state. That means you are drawing power during the off cycle, which is the longer period.

I just got a SS relay that is a ST - single throw, NO - normally open.

My project is based on a micro-controller with a real time clock. It will control relays/contactors to control lights and pumps as well as take temperature and humidity readings. (It can have a flood sensor for the occasionally accident and a light sensor for light monitoring. And it could monitor security sensors so you are alerted if someone gets in the grow room.) The information will be displayed on a PC and possibly a smart phone. Monitor your grow from work on your phone - now that would be a kick!

OverGrow the World !!


Monitoring from my iphone. Please don't suggest things like that! I won't be able to sleep until i've worked out how to do it!! haha

Yes i agree, the relay ON for the longer period is a bit silly. However, just today i got a delivery of a little fogger, and i've already made some changes. I'll go into more detail in a different thread regarding my build

I've changed it so that instead of switching ON/OFF i've got it switching between 2 outlets. I have connected it to a hybrid DWC/Fogger system. Fogger is ON for 30secs (enough to fill the container with fog) then the relay switches the power over to the air-pump for 3mins, which in turn drives all the mist up through the root ball! bingo!

I'm just waiting on the silicon to dry, and i'll fill it with water and take some photos for the other thread. I'm eager to see how long a lifespan i get with the fogger, i've got spare membranes and as long as they last 1-2 weeks, then i'm happy


Well-Known Member
Great adaptation. We need more DIY electronic projects.

Will follow your project closely - Good Luck!

OverGrow the World!!


Yea I know I'm resurrecting the dead (thread) here. But for anyone who tries this w/ a 555, please note that you need protection diodes wired backwards across the relay. When the contact on the relay's coil opens, there is a mag. field "held" in the coil which gets dumped back into the circuit and could potentially fry the 555 or other components. Im a programmer not electrician, so try something like this.

We definitely need more electronics here, so please keep posting everyone! I'm working out my own microcontroller project as well (fully configurable sprayers, fog, airstones, and fan in a cloner with data logging via a temp/humidity sensor all hooked to a pc; flowering setup is next on my list.) Anyone interested in this sort of thing check this site out. They have everything you need to a complete setup with microcontroller brain, IPhone/Android/webserver stats & control, and total data logging

[edit] ok, now I feel dumb. I just looked at the schematic and realized there is a diode there


i'm gonna try to build this circuit in days, this is for the project that im doing in the present.. switching on/off the pump.. for every 4minutes in like 30seconds.. hopefully it will turn out very very well.. this will be my first time building this kind of circuit.. do you have any tips or precaution that is a must, that has to be taken into account before anything bad happens? haaha.. :) but yea thanks for sharing..