Strange problem with STAMP and transistor switches!

I've built a paddle-shifter controller for the electronically controlled transmission on my car, but it seems to be having a bizarre issue that came about after about a month of use operating properly.

Basically, there are two shift solenoids, solA and solB, and one lockup solenoid. All three are electronically identical, being 10-15ohm solenoids. They are activated by 12v signal coming from the control unit (as the solenoids are grounded in the transmission)

The control unit itself controls the gear shifting by way of a BASIC Stamp controlling transistor switches--the unit automatically starts in first gear (solA on, solB off), and can shift up to second (sol A on, solB on), third (sol A off, solB on), and fourth gear (sol A off, solB off).

My current problem at the moment is as follows: after about 10 minutes of normal driving, shifting between the gears, 4th gear ceases to engage. Specifically, solB won't shut off when the output on the Stamp controlling that solenoid goes low. The pin is going low, so says DEBUG, but solB is staying on. Whats strange about this however, is that 1st gear works-- (solA on, solB off). What's also strange is that it used to work, and now, it for some reason has started to have this problem. And if I power it off, and let it sit for a while, it works again. Is this heat related? Some errant capacitance or something?

Here's the output circuit I'm using. There's three of these, one for each solenoid:

1K ___ .-|___|-o------o +12V | | | |< E NTE11 o----B| | |\C |/C | IN oB| NTE12 | | >E o------o Solenoid | | | - .-. ^ 1N4001 | | | 150 | | | '-' | | | '-------o | === GND

Any ideas as to what's causing this strange issue?

Thanks for any help!


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Can you probe the circuit in this error condition? I mean is it an electricla problem or mechanical? I assume the solenoids have a spring return?

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Hello Chris! Try asking this question is which gets more traffic and also post your full schematic in alt.binaries.schematics.electronic newsgroup.


Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

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void _-void-_ in the obvious place

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Boris Mohar

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with a V(CE)sat of 1V and a dissipation of 750mW the NTE11 can only handle

750mA continuous.

replace the NTE11 with a transistor that's rated for 1.5A continuous.

this'll probably mean something in TO126 or TO220 outline, and possilby a heatsink. I'd use a BD682 because they are reaadily available here.

Bye. Jasen

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Jasen Betts

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