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Circulating Timer Module

Very cheap and easy to use

by Julian Edgar

Click on pics to view larger images

At a glance...

  • Pulse lights, horns, buzzers, intercooler water sprays and more!
  • Adjustable ‘on’ and ‘off’ times
  • Output turns on as soon as power is applied
  • Relay output
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Here’s a great electronic module that can be used to pulse an output. It is widely adjustable, with both the ‘on’ and ‘off’ times able to be set separately. It uses a relay output that is able to drive high current loads (up to 10 amps). Finally, it’s incredibly cheap – less than $10 delivered to your letterbox!


The module is available from China through eBay. Do a search under ‘12V DC Circulate Time Delay Relay module’. Including postage to Australia, its cost was just under $10. 

The module

Click for larger image

The fully constructed module is about 56 x 30mm. At one end of the board it has inputs for power and ground, and the other end has three relay connections – one for common, one for normally open and the other for normally closed. 

There are two pots mounted on the board – one controls the ‘off’ time and the other the ‘on’ time. 

A red LED glows whenever power is applied, and a green LED turns on when the relay is activated. 

There is also a configurable link on the board. In a very tricky move, placing the link on the board feeds 12V to the ‘common’ terminal of the relay. This makes wiring much simpler in many applications, because the load can be connected between the other relay terminal and ground (more on this in a moment).

The board is well made and a quality relay is used. 


Click for larger image

The easiest way to see how the module works is to connect power and ground to the appropriate terminals. Rotate both pots fully anti-clockwise. Turn on power and the red LED will immediately light. With the pots set as described, the green LED will flash (and the relay) click, with the ‘on’ and ‘off’ times both being 1 second. This is the shortest output time available. 

Rotate the ‘off’ pot a fraction clockwise. The output will still be activated for one second but this might occur now only every 5 seconds. And if for example you wanted the output to be activated at 5 second intervals for the longer period of 10 seconds, you’d turn the ‘on’ pot a little more clockwise. 

You can see that both the frequency and duty cycle can be adjusted in this way. 

On the sample module, the ‘off’ time was adjustable from 1 – 120 seconds, and the ‘on’ time from 1 – 40 seconds. 

When the pots are adjusted correctly for the application, a dab of nail varnish can be used to hold them in the chosen positions. 


Click for larger image

This pic shows the easiest wiring connections, where a lamp is being flashed. Power and ground are connected as shown. The light is wired between the normally open terminal of the relay and ground. The link (arrowed) is in place that directs +12V to the common terminal of the relay. The light then flashes whenever power is applied. 


There is a multitude of uses in performance car applications:

- Water/air intercooler pump (off boost use the module to operate the pump for 15 seconds every minute, greatly extending pump life)

- Intercooler water spray (when on boost use the module to operate the spray pump for 5 seconds every 15 seconds, much reducing the need for  a large water tank while still giving very effective core cooling)

- Pulsing of lights, sirens or horns for alarm purposes (add a 20 amp relay if the current exceeds 10 amps)

Wherever you want to pulse an output, think of this handy module!

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