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I have a very old printed circuit board here that is used to control 2 pneumatic cylinders. There are 8 solenoid valves that control if the air goes in or out to a side of the cylinder.

Now the printed circuit is old and needs to be replaced, so I am trying to rebuild it with an Arduino.

The only strange thing I noticed was that there are only 4 NPN transistors (TIP122's), which I assume work as a toggle switch, the air can go in or out of each side of the cylinder.

But how is this done? I can't really create a schematic because the printed circuit is completed glued up.

JustJeff
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Roger Far
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  • guessing here, b/c it really is hard to tell what you're working with - but those things probably work in pairs; you'd let air in on one side of the piston at the same time as letting it out on the other side. So 8 valves could be controlled with 4 control signals. But unless you give the details of the problem, you won't be able to get a detailed answer. – JustJeff Mar 25 '12 at 01:34
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    @OlinLathrop - He's Dutch. Schema = = diagram in Dutch (Nederlandish? :-) ) – Russell McMahon Mar 25 '12 at 06:29
  • You could trace out the pneumatic "air circuits" easily enough and give a better picture. Cylinders may be double acting with air being admitted at end "A" and exhausted at "B" or admitted at "B" and exhausted at "A" – Russell McMahon Mar 25 '12 at 06:31
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    @Olin - Like Russell says he's Dutch. Don't expect everybody to speak flawless English. I would agree with your comment if it was sloppiness by a native speaker. – stevenvh Mar 25 '12 at 06:35
  • Sorry for my English but I am not into the used words for these kind of things. With Print I mean the print, yes it has some PIC's on it to control it with a joystick, which then control the NPN switches. – Roger Far Mar 25 '12 at 09:20
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    @JustJeff, Olin - Yes, "print" is Dutch shorthand for "printed circuit board". I guess OP doesn't realize it makes no sense in English – stevenvh Mar 25 '12 at 12:28
  • There, hope the OP is OK with that edit. It can always be rolled back. I was tempted to replaced 'glued up' with 'potted', but let that ride. – JustJeff Mar 25 '12 at 13:16
  • @OlinLathrop, It hurts nothing to be a bit more kind, please try to in the future. He did take the time to attempt to write a good question with a few mistranslated pieces. – Kortuk Mar 25 '12 at 16:46
  • What do you call the printed circuited? So the commonly green piece of plastic with copper lanes on it? – Roger Far Mar 26 '12 at 14:04

1 Answers1

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You could trace out the pneumatic "air circuits" easily enough and give a better picture. BUT there is a good chance that it works as follows:

Cylinders may be double acting with air being admitted at end "A" and exhausted at "B" or admitted at "B" and exhausted at "A". This could easily be controlled with 4 transistors, with each transistor activating an inlet solenoid at one end and an exhaust solenoid at the other end simultaneously.

Q1 Inlet 1A, exhaust 1B
Q2 Inlet 1B, exhaust 1A
Q3 Inlet 2A, exhaust 2B
Q4 Inlet 2B, exhaust 2A

Cycling: Q1 on - pause - Q1 off, Q2 on - pause, Q2 off .. repeat
will shuttle cylinder 1 to & fro.

Simiarly Q3, Q4 control cylinder 2.

Added:

4 NPNs seems rather reasonable - you have only 4 inputs with two NPNs being on at a time. as above. But, ...

Instead of transistors you could use 1 x ULN2803 IC or similar. Datasheet here - 8 darlington drivers in one IC.

Use 4 channels just as for transistors

Nominate one side of each solenoid as below.
Connect either side of each solendoid to V+.
Connect pin 10 of ULN2803 to V+
Connect pin 9 of ULN2803 to ground.
Go!

Q1 Inlet 1A, exhaust 1B Q2 Inlet 1B, exhaust 1A Q3 Inlet 2A, exhaust 2B Q4 Inlet 2B, exhaust 2A

You can pair up 2 ULN2803 channels for extra drive.

Russell McMahon
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  • That's what I figured from tracing the print, but could you give a small example how this should be connected with an external power source? Or will I be bound by 8 NPN's then? – Roger Far Mar 25 '12 at 09:22
  • 8 NPNs seems rather reasonable - you have only 4 inputs with two NPNs being on at a time. as above. Instead of transistors you could use 1 x ULN2803 IC or similar. Datasheet here - 8 darlington drivers in one IC. – Russell McMahon Mar 25 '12 at 11:54
  • @Rogier21 - Serious questions: Afraid of what? You have to connect power SOMEHOW. How would yu hope to connect to an external power source without using some sort of switch? The NPN transisors or driver IC are just an electronic switch. Please explain what you HOPEDd a solution would look like. Use enough detail to allow us to follow your thinking and don't just say eg "connect to". – Russell McMahon Mar 27 '12 at 02:42
  • I just asked, how can I connect 8 solenoids with 4 NPN transistors, with an external power source. I know how to use the NPN as "double acting switch" without an external power source, but not with. – Roger Far Mar 27 '12 at 08:49