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Bidirectional motor controller

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BOB KIRK

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Hello,i want to make a automotive servo motor tester. I need to know how to interface a 555timer with a l2722 dual opamp. I have the schmatic of the one i took out of the car.Any help greatly appriciated.thanks bob
 

MikeMl

Well-Known Member
Most Helpful Member
After you figure out how, post the schematic:D
 

MikeMl

Well-Known Member
Most Helpful Member
Hi Bob,

Looking at the traced out automotive schematic, I see only a bridged DC amp which can reverse the motor; nothing to do with PWM. When you say you want to use a 555 in your tester, do you want to create a PWM drive for the motor?
 

BOB KIRK

New Member
servo tester

Hi Mike, i replace a lot of the servo motors in auto a/c repair work. If you see the 5 pin plug [LOWER LEFT] the logic is suplied by the automatic climate control system via sensors/software.Could i use a pic controler with right program to operate this device? I'm trying to learn to instruction set for the pic but i'm not a programmer by a long shot! Thanks Bob
 

MikeMl

Well-Known Member
Most Helpful Member
You can do lots of things with a PIC. However, back to the circuit you posted. You didn't comment on the Pulse Width Modulation (PWM) question.

What signal is at "#[email protected]"? Where does it come from? Is it a triangle wave or ramp?

Have you seen this?
 
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BOB KIRK

New Member
Servo theory of operation

Hi again Mike,thanks for taking the time to talk to me.If you would go to ALLDATAdiy.com :: Leading Source of Diagnostic and Repair Information AND LOG IN UNDER KIRK1952 password is PASSWORD.Under "vehicle subscriptions" select 2003 gm denali, third one from the top.Select "heating and airconditioning" then on right side select discription and operation for automatic system. You can read the theory of operation.Not sure about pwm.the 555timer is what i'm familar with,thought it would work.Signal on pin 6 is explained under theory.By the way i drew the schmatic myself from pc board with magnifing glass. Thanks again Bob
 

MikeMl

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Most Helpful Member
Hi Bob,

Here is what I read:

"Mode Actuator
The mode actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5-volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5-volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts . A 0 or 5-volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts .

The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded or targeted value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates, the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts .
"

Do you want to build a tester just for the motor-actuator, so that you can remove it from the car and plug it into your tester on the bench, and then run the motor through the limits of its travel?

If so, what connections are on the motor-actuator?
Just the two motor leads?
Or is there some sort of position feedback signal?
Pot?
Limit switches?
What happens if you drive the motor until it hits either end of its travel?

Creating bidirectional drive for just the motor/actuator could be as simple as a 12V DC power supply and a center-off, double-pole, double-throw switch, so I am puzzled about how much of the schematic you posted you want to duplicate?
 
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BOB KIRK

New Member
Servo

Hello Mike, remove the actuator from the car and plug in to bench tester is the goal. I think for pin #6 &9 all i need is a variable resistor. wire pot for 0 to 5 volt control and a 5 volt reference.The pot on right side of schmatic is shaft connected for positioning signal.Will this work? THANKS bOB
 

MikeMl

Well-Known Member
Most Helpful Member
Here's something that cobbled up. Based on your diagram and the description of how it works, I start with a 12V Power Supply with reasonable regulation with sufficient current to handle the motor. I use an LM7805 to produce the 5V ref. I use a 5K pot to let you set a desired position to drive the motor to. I use an TLC2272 opamp to subtract the feedback actual position Vp from the commanded position Vc and amplify the difference, which is called ERROR.

Suppose you set the 5K Pot so that Vc=4V. Further suppose that the motor is sitting such that the Position Pot inside the DUT is at 3V (Vp, DUT pin9). This will cause the opamp output ERROR to rail at 0V, which will run the motor in the direction so as to drive the internal pot to a lower voltage. As the motor drives the internal pot close to 1V, ERROR begins to move toward 2.5V, which causes the motor to stop. Regardless of what you set Vc to, the motor will run until Vp = 5 - Vc (and ERROR = 2.5V).

The Feedback resistor RF sets the gain of the difference amplifer. The higher the value, the higher the gain. If you set the gain too high, the motor will oscillate back and forth around the set point. If the gain is too low, the motor will stop too soon.

One possible screw-up might be that the polarity of the position feedback signal on DUT-pin9 is backwards relative to my assumption, in which case the motor will drive away from the commanded position until it hits on stop or the other. If this happens the fix will be to invert the feedback signal before it goes into the subtractor. If needed we have an used half of a TLC2272 to fix it :D
 

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BOB KIRK

New Member
My servo test gig designed by MIKE

Hi Mike.i really want to say thank you for your time and of course you knowlege and perfessionalism! I envey you so much,because i love doing this kind thing even i don;t fulley understand it quite YET! I WILL ENDEAVER TO LEARN! I was an analog bench tech reparing test equiptment the old simpson&tripplet multimeters.And calibration.6 years Marine Corps.I got a crash course in fundamentals of digital logic in the mid 70s.but got real interested about 10/12 years ago with first good computer.With help from professionals like yourself its alot of fun.I will build this circuit as soon as i get some free time,pretty busy with airconditioning business now.Thanks again your friend BOB KIRK


PS I would like you to explain how another circuit works, its diode logic i think,i will send attachment asap
 

BOB KIRK

New Member
On off switch/led

Hello mike,in the attachment/please tell me were the ground is for the led and what the other paralleled diodes do_On the green wire there is 12vdc positive/doesn't this reverse bias the diodes.Confused Bob
 

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MikeMl

Well-Known Member
Most Helpful Member
Hello mike,in the attachment/please tell me were the ground is for the led and what the other paralleled diodes do_On the green wire there is 12vdc positive/doesn't this reverse bias the diodes.Confused Bob
Its hard to tell what is going on in this partial schematic, but I will make a few assumptions. I'm guessing that the black line 8 at the top has +12V on it. If the fuse is intact, then that puts +12V on the blue-red line and on the left end of the A/C and DEF switches. If either switch is closed, then that puts 12V on the Yellow line and the anode of the LED. If the GREEN line has a path to 0V (sometimes called Ground ;) ), the LED will light.

Now, here comes some speculation on my part. I'm guessing the network consisting of the two diodes and three resistors between the cathode of the LED and the Green line is first to limit the current through the LED, and make it dimmable. I'm guessing that the Green line is actually connected to a dimmer bus elsewhere in the car. If you have ever tried dimming an LED in parallel with a standard incandescent lamp, you will know that they have very different dimming curves; so I suspect that the diodes and resistors tailor the dimming curve of the LED to more closely track the dimming curve of incandescent lamps.:D
 
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