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Help designing switching circuit...

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Zeez

Automotive
May 2, 2004
4
This is kind of hard to explain...especially at 2:00 AM. :) The transmission in my truck is completely electronically controlled. It's an automatic, but I'm turning it into a part time manual.

What I want to have is a control somewhat like in race cars - two momentary buttons, one for up shifting and one for down shifting.

My trans is controlled like this:
SOL1 SOL2
1st On Off
2nd On On
3rd Off On
OD Off Off

Does anybody have any thoughts about where to start designing a circuit that would allow me to switch those solenoids on and off, using only two momentary buttons?

Thanks!

 
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And just what transmission is this? This is a very nice logical function. But, from the transmissions I've worked on, I don't believe it for a second. Even transmissions I've seen with six solenoids don't have the ability to control the shifts that well. Start with getting an ATSG manual at
 
This is a Jeep AW4 transmission. It is also used in Toyotas and Landcruisers. And yes, it is completely controlled as I posted.
 
As Opera said; this is an elementary logic function.

You need an up/down binary counter (two stages) and also debouncing for your switches. Arrange the switches so that the counter counts up one when the up switch is actuated and down one when the down switch is pressed. You have to make sure that the counter does not wrap around from state three to state zero and vice versa. Do that by decoding the zero state and block the down switch and also decoding the three state and block the up switch (the decoders will act like limit switches - in a way). These two decoders will also be used for two of your solenoids.

Two more decoders are needed for state one and two and control the other two solenoids. There shall be drivers or transistors if your solenoids need some current - and I am sure they do.

You could also talk to someone that can do it in a small micro for you. It should not take many hours to get it up and running.
 
May I add a cautionary note, I once designed a logic circuit to replace a broken sidelight/headlight switch on my car with (debounced) push buttons which operated high current relays. It worked fine on the bench but when I wired it into the car I found that starting the car triggered the logic circuit into some random state - switching either the sidelights or headlights on! I think this must have been due to the battery voltage drop caused by the high current drawn by the starter motor and/or current spikes as the starter motor turned. You don't want your circuit to suddenly select a gear for you while you are starting the engine!

Dave
 
Yes, dhwilliams.

I forgot to mention that you need a reliable power on reset (POR) circuit that puts the counter into neutral state when turning on. Hmm... I think that you will need a five state counter then. So you will need three binary stages (counts 0 1 2 ... 6 7) and decode state 1, 2, 3, 4 for the solenoids. State 0 is the idle state and also the power-on state.

I think that a micro will be the better choice after all.
 
I questioned the two solenoids. Though not familiar with this AW4 / A340 transmission, my understanding is that it has three solenoids. The extra being the torque converter lockup (usually 3 & 4). I understand the desire to do somethig trick (my transfer case has 2WD LOW). Unless you are doing something really trick, there aer a number of lockout functions that are desireable to add. This would be a neat project for a little Microchip in Control Basic for about $200. That is simple enough for a first time programmer and you could add some great functions. If your budget is bigger and you want really nice, check Bauman Engineering.
 
Thanks for the help guys.
 
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