Go Down

Topic: circuit for automatic air organ (Read 1 time) previous topic - next topic


Hello everybody,
together with my dad we are creating an automatic air organ.
Here you'll find an older picture. Right now
we are, except for the electronics, almost done and it contains 3 of those boxes with pipes and built in solenoids.

I would like to let multipcb create my board which I'm creating right now in eagle. But my experience in eagle and PCB's is none. I only have experience in experiment boards...Could anybody have a look at my schematic?

The schematic
On the top left site you'll find the outs of an arduino. Because I want to have the possibility to open the solenoids very slowly I want to use PWM. Since arduino does not have enough PWM, I use the TLC5940, thanks to Acleone's Library. How to connect it you'll find here.
And here are the eagle files.

This is the solenoid, a special
one for air organs.

Here are my most important questions:
- I have 8 warnings in eagle. This are the two different ones:
 "POWER pin U$1 IREF connected to N$1"
 "POWER pin U$1 VCC connected to +5V"
 "Part jp1 has no value" (I thought the JPt is just a block were you can put pins in, don't get it)

- If I look at this schematic, the solenoid is before the collector. That's unpractical for me, can't it be after the emitter?I just hear something about mosfets, I have to check that out...don't know them.

- The previous schematic uses tip102, I was told to use tip122 but now I don't understand why I don't use tip102. maybe a mosfet is the answer....

- I tested the solenoid on PWM and it works great, but on the solenoid itself there is a p6ke diode. Not a shotky...should I replace them anyway because I use PWM?

- I'm a bit worried about the speed. I used one tlc before to control lego motors with max/msp. It worked fast but I don't know what will happen if you use 3 tlc's and so many out's. I also want to use max/msp in the end for this project...I want it to have a not noticeable latency of course....

thanks in advance!


Hi Yurk;

I've never laid out a PCB either so I can imagine this has been quite a project for you to take on. One point I would make is that the 24vdc solenoids you are using only draw 90ma of current so you don't need such high power switching transistors. Logic level MOSFET devices should work just fine and save a lot of components and space on your driver board. I think board size has a lot to do with board costs also.

The popular 2N7000 is a very inexpensive device in a TO-92 package:




The schematic shows an NPN transistor.  If you want to put the solenoid between the transistor and power use a PNP transistor (though that will be turned on with a "0" output).  That swaps the position of the emitter & collector in the circuit.

To way oversimplify, the rule of thumb is to always put the load on the collector side of the transistor.  If the load is on the emitter, it can change the voltage the emitter "sees" and cause erratic behavior.  If you put it on the collector side, then you are OK as long as the base and emitter voltages have the right relationship.  

I agree the transistor doesnt need to be huge.  I use PN2222/PN2907 (small switching transistors) for relays and have no problems with heat.   Using too small of a base resistor is going to burn them up easier than too much load.

"Electrical Engineering 101 - everything you should have learned in school but probably didnt" by Darren Ashby has the best intuitive explanation of this that I have ever seen.  Unfortunately the last third of the book is how to deal with engineering managers.....


That organ looks like the sort of thing they make at the Early Music Centre in Bradford, not too far from where I am now.

Why are you using TLC5940s? Do you need the PWM capability of it to proportionally open the relays? If not then there is no advantage in using them.
What is more because you have a higher voltage than the supply I think you need to clamp the output to the rail. There was an application note about this but I don't have it to hand.

Before you delve into making a PCB then do try at least one channel works first. Personally I wouldn't bother with a PCB at all and I would make it on strip board.


Power Shift Registers might make more sense...

Like maybe these:  L9822E

Available from Mouser

Go Up