A simple automation circuit

Thread Starter


Joined Oct 22, 2016
This should be simple, but not for me. This is for a DIY edge bander.
I need a circuit using switches and relays to control a feed motor and cutter.
The feed motor is controlled with a contactor. The cutter is pnuematic and controlled by a solenoid.
The feeder is energized and pushes a board down a table applying 'tape' to the edge. The leading edge of the board encounters a SPDT switch embeded in the table top and pushes the contacts in. The feeder continues push the board down the table until the trailing edge of the board causes the switch to retract, which stops the feeder and activates the solenoid that activates the pnuematic ram to cut the tape. As the tape is cut a SPST switch opens to de-energize the solenoid to allow the pnuematic ram to return. At the same time the feeder motor is re-energized and the process repeats.

Besides the above mentioned switches, I believe the only other device needed would be a DPDT relay. That being said I have spent two days trying to draw the circuit with no success.

Any suggestions?



Joined Mar 14, 2008
Post a diagram of all the components to be controlled.
Then make a clear list of all the sequential steps that occur (not in paragraph format).
For example, "the feeder is energized" doesn't tell me how that occurs.


Joined Oct 30, 2015
Seems to me that you need a state machine much more complex than a simple set of switches, solenoids and relays. Even if you only use these components, you will need some kind of timer to ensure the different steps of the actuation occur at the right time. For example, I can see the switch enabling the feeding motor until the edge is found. This is easy! However at that point in time the solenoid must be activated to cut the band. If you use the feeder motor enable switch as your signal, you will need some sort of single shot timer because other wise, whenever the feeder motor is not enabled, the solenoid would be enabled (at all times) and I doubt this is what you want.

Seems to me you need some kind of controller, albeit a very simple one. This can be done so easily with microcontrollers. That may of course even be more complex for you, so my recommendation is to pair up with some microcontroller geek. I tell you, this is a 30 minute project for anybody with enough MCU experience. You can also do it with 555 timers and I imagine somebody in here will mention that. I personally prefer solving most timing problems with MCU's as it is way easier.

Good luck on your project!


Joined Jun 22, 2012
What are the voltages and currents of the edge bander, solenoid etc, this will give you a better idea of component selection, it can be done with contactors and timers....?

Thread Starter


Joined Oct 22, 2016
Yes, it is just the low voltage circuit (12vdc) that I was having problems with. The high voltages would be controlled through a 'contactor/solenoid' which are shown only as 'feeder/cutter' in the drawing.
The OP described what I saw a machine doing on a video.

I was able to come up with my own design using a SPDT relay and the aforementioned switches.