Cascading relays - demonstration purposes only

Thread Starter


Joined Jan 21, 2011

I have three electro-mechanical relays - the type used in old telephone exchanges (Strowger). Rather than collecting dust, I'd like to display them "actively" - doing something.

My plan is to wire them up, in a cascading style... Press an 'on' button, relay1 energises, lights a lamp. After a small time (1 sec?), relay two is energised (by relay1), lighting a lamp (with relay1's lamp still lit). Then after the same duration (1 sec), relay3 is energised lighting its lamp. Now all three relays are energised and all three lamps are lit. then, after a period (let's say 5 seconds), all three relays de-energise and all three lamps unlit.

The process starts again with a push of the 'start' button (momentary button).

Voltage not too important - 12V / 9V (battery operated).

I know the relays will have to be wired to be self-latching, and ideally I'd like to use discrete components if possible (caps / resistors / diodes) - without chips. But if it's easier with a chip or two, then that's fine.

The main point is to demonstrate what the relay does / how it works, complete with the "click" when the relay is energised.

Thanks in advance,


Joined Mar 10, 2018
Natural for an Arduino to implement sequence, and a driver to handle
the relay currents (how much does a relay take for current ?). Driver
could be a mosfet per relay, or a open collector relay driver. Videos
on web to learn mBlock. Board cost ~ $ 2 - $6 depending on board

Using mBlock to program Arduino -

mBlock is free, just download it. Drag and drop blocks, then when finished
mBlock generates Arduino code and uploads it to Arduino board.

Regards, Dana.


Joined Mar 10, 2018
I forgot the click, thats just another pin used to drive a speaker,
buzzer, and in mBlock just pulse the speaker/buzzer once to get "click" -


Regards, Dana.


Joined Aug 1, 2013
OR - Two chips plus whatever it takes to drive the relay coils. One Schmitt trigger gate chip and one shift register chip. The nice thing about the shifter is that you don't have to wire the relay contacts to get the latch-on function - the shifter outputs holds each relay on until the cycle ends. The gate chip, such as a CD4093 quad NAND, is both the oscillator and the control logic. One-two hours to wire it up on perf board, depending on your skill level. No programming.

What are the voltage and current ratings for the relay coils?

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