Building a four channel SolidState Relay

Picture of Building a four channel SolidState Relay
For an Arduino project I needed to switch 4 mains devices.
I am always deliberating wether to use a mechanical relay or a solidstate relay.
Solidstate relays used to be relatively expensive, and thus people constructed them from opto couplers and triacs, but there are some cheap SSR chips available. One of my favorites is the 39MF22 that is available for  1.80 euro. So I made a choice to build a solid state relay for my project.
I have to add though that a four channel relay board, ready made, is also not that expensive. So, before you build my solid state relay you may want to check out these options: or even cheaper: . In fact, these may even be slightly less expensive than the Solid state relay board I will be describing here.

Bill of materials:
4x 39MF22 from e.g. dickbest  I believe it can switch 900 mA which is sufficient for most of my applications You could also use PR26MF12. It is pin compatible and switches 600 mA
4x 8 pins dil IC holder
4x LED in color of choice
4x 330 Ohm resistors
4x 2 pins screwconnector
1x 5 pins female header
1x 5 pins male header 90degrees
1x Tic-Tac peppermint dispenser The bigger one: 8.5x2x5 cm
1x piece of PCB 6x4.6 cm

For a snubber:
1x 100 Ohm resistor
1x 100 nF 600 V resistor

OK Stop right here. This circuit is meant to switch AC loads of  110 or 220 Volt. These voltages can and will kill you, so be careful and if you do not feel confident you know what you are doing, you should only use this for low AC voltage loads.

Also, as said, this circuit is for switching AC, it is not for DC. for switching DC a HCT4066 should be considered (depending on the load to be switched)  or a mechanical relay
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gsandhu229 days ago

I’m working on a project which is about making a rescue
robot . I have struggling with it for 4 months and now all the mechanical works
had been done . but I’m facing difficulty in make the robot to work with rf
module can u plzz help me…

I want make transmitter and receiver that can control the
motion…I mean that receiver should have control 8 dc gear motor and each dc
motor should have a forward and backward botton to control the motion ……can u
kindly help me with this project ….if u can make the circuit board diagram for
the PCB ….or any other suggestion plz reply……mail me at “”

diy_bloke (author)  gsandhu227 days ago

synny, it is kind off a far cry from having questions on a 4 channel solid state relay and designing and building an rf controlled 8 dc back and forth motor project.
I dont want to be unfriendly but you are asking something here. Anyway, as I do not know your platform at all, I will make some suggestions what you can do.
RF transceiver modules can be picked up from for just a few euro's and can easily be controlled by a microprocessor. Presuming you are using a microcontroller in your robot, you can buy again for a few euro, a 2 or 4 channel motordriver from in which you can reverse polarity. you need either 4 or 2. hook these up to a pin of the microprocessor and you can control direction. If you also need to control speed you need 2 pins per motor.

Hook up the receiver and let your program take actionon the motors according to what you send.
Attach the transmitter to another microprocessor, or just to buttons, depending on how sophisticated you want to make it and off u go.

Amother possibility is to buy a ready made transceiver set like for model planes, with the amount of channels you need

Good luck

tiger52487 months ago
I looked up the data sheet for the DIP used here (39MF22). My question is can this really switch 120+ low current voltage? I simply don't see that in the data sheet, but I could be wrong. I would like to use this circuit to switch christmas lights that I am working on. Do you think this will work with one strand of normal christmas lights?
diy_bloke (author)  tiger52487 months ago
Though I cannot try it myself as i have no 120 Volts, I see no reason why it should not. The low current should not make a difference
Ben J1 year ago
I built your relay design into an Arduino circuit, but the relays don't seem to be working like SPST switches, like I expected (there is no continuity between pin 6 and 8 when the relay is activated).

Please forgive me, as I know very little about electronics - I simply cobbled together a few circuit designs I've come across (5V regulator, Arduino, MIDI input, and your relay design).
diy_bloke (author)  Ben J1 year ago
Ben, sorry for my late reply, I did not see your question come in. Well the 39MF22 is not exactly a single-pole, single-throw switch it is a solid state relay and the switching takes place with a triac.
When you say that thereis no continuity between pin 6 and 8 I get the impression that you just measured that with a multimeter and that will not give proper results.
You really need to see pin 6 and 8 as the poles of a AC current swith. Have you actually tried to swith an AC load with it?
Your picture looked impressive :-) even though i could not really see what was on it because of the burning LED's. Anyway, let me know what you are trying to switch and wether that is an AC load or a DC load
Thanks for the reply! :)

Yes, the LEDs are probably a bit too bright, especially that green power indicator.

The relay section will be connected to 1/4" TRS cables for switching channels on a guitar amp - thus, very small current. I'm a bit too gun-shy to do anything with AC at this point; I think I'm a bit of a novice to attempt anything as dangerous as that.

I could've used mechanical relays, but I was attracted to the smaller form factor of SSRs, as I'm trying to make the board as reasonably small as possible, so as to fit into a specific-sized hammond enclosure.

I'm learning things as I go along, and I was pleased with how things turned out, even though it's only a semi-functional circuit. That said, I'm glad that parts and DIY PCB fabrication are as cheap as they are. :)
diy_bloke (author)  Ben J1 year ago
I doubt if the channels on a guitar amp can be switched by a solid state relay, so that is where your problem lies. You do however now have a midi controlled lamp switch :-)
If you do not want to use small relays, use the 4066 (either a HEF4066 or a HCT4066) that is a bidirectional switch (4 per IC I think) that can be controlled with an enable pin
diy_bloke (author)  diy_bloke1 year ago
a HCT4066 costs about 0.25 euro and has 4 channels so that is cheaper than the 4 x 39MF22 (4x1.80) and probably smaller as well
diy_bloke (author)  diy_bloke1 year ago
If you are indeed switching DC then the 39MF22 is not suitable for that. It is better then to use e.g. a HEF 4066 if the current is not too big or otherwise a small reed relay
Farnell has the PR39MF51NSZF SSR for just over a £ in the UK.

The datasheet suggests that you might have problems with inductive loads (motors, solenoids) if the voltage rate of change on switching is high (< 100v per us) and suggests in that case a snubber (R and C in parallel) between pins 6 and 8 - they suggest starting values of 0.022uF and 47ohms - what works will vary with the type of load.

So if anyone has problems with erratic switching of motors, etc, they might want to experiment with different values of R and C between those pins.
That should have been "( > 100v per microsecond)", of course.
diy_bloke (author)  mikeatboduel1 year ago
Thanks Mikeatboduel. Netherlands is not the cheapest country where electronics parts (and many other things) are concerned. 1.80 euro's is about 1.45 pounds.

You are right with regard to the datasheet and switching inductive loads is the very reason why i always hesitate vetween a mechanical relay and an SSR. In another tutorial in which I use the 39MF22 I think I indicated use of a snubber network (100R/100nF). I think though it might be better to have that directly over the contacts of the inductive load. E.g. in a socket where it plugs in.

Having said that. I have been using the 39MF22 for some time already to switch pumps and that has not given any problems yet.

diy_bloke (author)  diy_bloke1 year ago
Let me just add that the 39MF22 is suitable for currents up to 900mA. The max load I have been switching with it was 100 wats and the max inductive load might have been 20 wats and that goes very well. If you'd want to switch a 198 wats (the max) inductive load, I would definitely use a snubber and probably a fuse as well, probably even choose a different relay.

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