DC Motor Driver with Limit Circuit Not Working

Thread Starter

John A Bonilla

Joined Mar 11, 2017
92
Hi Everyone,

I have the circuit that controls a dc motor using the L9110s motor driver. It is powered by a 1.5V AAA battery that is stepped up by the TI TPS61027DRCR TO 5V. The goal of this circuit is that when the ITR8307/TR8 Optical IR Sensor sees a white stopping plate, the motor no longer moves in the given direction.

I currently have the PCB assembled, however when I press the button to move the motor (the white stopping plate not attached), the motor is not moving at all. I increased the input voltage from 1.5v to 3v using a power supply in case I was maxing out the 200mA current draw, and I am facing the same issue. When I used an ammeter to measure the current flowing to the motor I got nothing 0.000A and originally when using 1.5V and applied a load the voltage would drop to 0V which I assumed meant that the TPS61 was being over demanded.

If anyone has any ideas as to what is wrong with my circuit I would be very grateful for any suggestions. One other idea I had was changing the circuit to the second picture to reduce components and potential complications. Thank you!
 

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sarahMCML

Joined May 11, 2019
370
Hi Everyone,

I have the circuit that controls a dc motor using the L9110s motor driver. It is powered by a 1.5V AAA battery that is stepped up by the TI TPS61027DRCR TO 5V. The goal of this circuit is that when the ITR8307/TR8 Optical IR Sensor sees a white stopping plate, the motor no longer moves in the given direction.

I currently have the PCB assembled, however when I press the button to move the motor (the white stopping plate not attached), the motor is not moving at all. I increased the input voltage from 1.5v to 3v using a power supply in case I was maxing out the 200mA current draw, and I am facing the same issue. When I used an ammeter to measure the current flowing to the motor I got nothing 0.000A and originally when using 1.5V and applied a load the voltage would drop to 0V which I assumed meant that the TPS61 was being over demanded.

If anyone has any ideas as to what is wrong with my circuit I would be very grateful for any suggestions. One other idea I had was changing the circuit to the second picture to reduce components and potential complications. Thank you!
Your opto-couplers are doing nothing in both versions of your circuit, except to apply 0V to both IA & IB in the first case, and possibly V+ to IA & IB in the second case (depending on whether the L9110 has internal pull-ups or not!). In either case the driver is in the "Apply the Brakes" mode.
 

Thread Starter

John A Bonilla

Joined Mar 11, 2017
92
Your opto-couplers are doing nothing in both versions of your circuit, except to apply 0V to both IA & IB in the first case, and possibly V+ to IA & IB in the second case (depending on whether the L9110 has internal pull-ups or not!). In either case the driver is in the "Apply the Brakes" mode.
Ok, if you don't mind how would you re-design the circuit to meet the original intentions?
 

sarahMCML

Joined May 11, 2019
370
Ok, if you don't mind how would you re-design the circuit to meet the original intentions?
I mistakenly thought that by the way the opto's were drawn that they were slotted switches. Looking at their datasheet I see that they are reflective types!
How is your setup arranged as hardware? Is the purpose to switch one of the 10k resistors high until the opto switch detects the white card, which then goes low and switches that side off, at which point you reset that switch, and can then use the opposite switch to drive back again?

The problem as I see it is that when not illuminated, the phototransistor's collectors are effectively open circuit, and so, unless, and even if, the motor driver has inputs which pull them high, you pulling your 10k resistors high with your switches is going to do nothing! You can never pull either input to 0V!

Your second circuit may work, although you may need a pull-up resistor on the collector of Q1, and possibly a high value (100k) pull-down on its base.
 

Thread Starter

John A Bonilla

Joined Mar 11, 2017
92
I mistakenly thought that by the way the opto's were drawn that they were slotted switches. Looking at their datasheet I see that they are reflective types!
How is your setup arranged as hardware? Is the purpose to switch one of the 10k resistors high until the opto switch detects the white card, which then goes low and switches that side off, at which point you reset that switch, and can then use the opposite switch to drive back again?

The problem as I see it is that when not illuminated, the phototransistor's collectors are effectively open circuit, and so, unless, and even if, the motor driver has inputs which pull them high, you pulling your 10k resistors high with your switches is going to do nothing! You can never pull either input to 0V!

Your second circuit may work, although you may need a pull-up resistor on the collector of Q1, and possibly a high value (100k) pull-down on its base.
So I believe your description of how the device works is correct. I have made a simple diagram in the picture attached. In your last post you referenced that the second circuit may work, however you mentioned that Q1 may need a pull-up resistor, however in the second circuit both q1 and q2 are removed. Could you clarify what you meant? Thanks for the help!
 

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sarahMCML

Joined May 11, 2019
370
So I believe your description of how the device works is correct. I have made a simple diagram in the picture attached. In your last post you referenced that the second circuit may work, however you mentioned that Q1 may need a pull-up resistor, however in the second circuit both q1 and q2 are removed. Could you clarify what you meant? Thanks for the help!
Somehow I got the 2 diagrams mixed up, I meant the circuit which had the transistors Q1 and Q2 would work, with the modifications.
What stops the carriage at either end of its run?
I have to go now, so may not get back for some hours.
 

Thread Starter

John A Bonilla

Joined Mar 11, 2017
92
Somehow I got the 2 diagrams mixed up, I meant the circuit which had the transistors Q1 and Q2 would work, with the modifications.
What stops the carriage at either end of its run?
I have to go now, so may not get back for some hours.
No worries, the idea is that when the sensor sees the "white card" it disables the function. For example:

User Presses (and holds) the down button ->
The white card moves down the pole driven by the dc motor ->
the bottom sensor (Key2) sees the white card ->
the npn sensor's transistor opens, thereby pulling the circuit to ground ->
the motor stops moving and the down button no longer functions. ->
The up button is available for the user to raise the white card up ->
when out of sensor range the white card can move up or down based on user input.

I hope this clarifies my goal.

I updated my schematic to use a 100kOhm pull-down resistor as you suggested, I was unsure of the size resistance to use on the pull-up resistor.

Let me know if you think this looks good!
 

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MisterBill2

Joined Jan 23, 2018
18,442
I see no circuits to follow. I see collections of individual elements that might possibly connect to other elements, BUT NO CIRCUIT IS SHOWN. I don't know where the concept of showing separate blocks came from, but it is a poor choice for presenting a circuit to follow and understand what is going on.
I suggest sterting with evaluating the operation of the motor driver, identified as U6. Is it intended to function as an H-bridge, connecting one side of the motor to positive and the other side to negative?? The very first step in diagnostics will be to see if the motor driver even makes the motor move. The next step will be to see if the control circuit parts actually do what you want them to do, as far as output voltages .
 
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Thread Starter

John A Bonilla

Joined Mar 11, 2017
92
I see no circuits to follow. I see collections of individual elements that might possibly connect to other elements, BUT NO CIRCUIT IS SHOWN. I don't know where the concept of showing separate blocks came from, but it is a poor choice for presenting a circuit to follow and understand what is going on.
I suggest sterting with evaluating the operation of the motor driver, identified as U6. Is it intended to function as an H-bridge, connecting one side of the motor to positive and the other side to negative?? The very first step in diagnostics will be to see if the motor driver even makes the motor move. The next step will be to see if the control circuit parts actually do what you want them to do, as far as output voltages .
The individual elements are connected via net-labels (Common schematic design practice) to keep the parts of your circuit neat and easy to read.

In reference to your other comments, U6 is an h-bridge used to drive the DC motor attached. I’m unsure what you mean by connected to positive and negative, as indicated by the data sheet 5V and ground is to be supplied to the corresponding pins. The logic for whether the motor is driven clockwise or counter-clockwise is represented as IA and IB. Finally the motor outputs are connected. I’m unsure what the confusion is regarding its setup.

Your last comment regarding testing, I did preliminary testing which is where I found that while the circuit did supply 5V and -5V to the motor when the respective button was pressed, if I applied a load the voltage would drop to zero. I did testing with an Ammeter to determine if any current was flowing to the motor which resulted in no current flow. I have come up with a few hypothesis but they were unfortunately wrong. That is the reason I came here for help.

If you have any constructive suggestions I would be more then happy to put them to the test. Thank you
 

MisterBill2

Joined Jan 23, 2018
18,442
EVERY ONE OF MY COMMENTS WAS INTENDED TO BE CONSTRUCTIVE!!
NONE of my clients, nor myself, would accept a drawing like that, which is to be used for construction, service and evaluation. It might be OK for circuit boards but totally unuseful with wired circuits. That would be fine as the input for an auto-router to design a circuit board.Plant electricians do not have time to trace out netlists.
And now, if the driver is not sending current to the motor, the question arises as to what is the problem. I will need to examine the data sheets to discover that. Is it possible that it is made for a higher voltage application??
 
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sarahMCML

Joined May 11, 2019
370
No worries, the idea is that when the sensor sees the "white card" it disables the function. For example:

User Presses (and holds) the down button ->
The white card moves down the pole driven by the dc motor ->
the bottom sensor (Key2) sees the white card ->
the npn sensor's transistor opens, thereby pulling the circuit to ground ->
the motor stops moving and the down button no longer functions. ->
The up button is available for the user to raise the white card up ->
when out of sensor range the white card can move up or down based on user input.

I hope this clarifies my goal.

I updated my schematic to use a 100kOhm pull-down resistor as you suggested, I was unsure of the size resistance to use on the pull-up resistor.

Let me know if you think this looks good!
Something else I missed due to concentrating on the opto circuits specifically was that the outputs of the 2 transistors Q1 & Q2 should connect to the IA and IB pins on the motor driver chip, not motor Gnd, which should be 0V.
For the pull-ups try 1k.
 

Thread Starter

John A Bonilla

Joined Mar 11, 2017
92
Something else I missed due to concentrating on the opto circuits specifically was that the outputs of the 2 transistors Q1 & Q2 should connect to the IA and IB pins on the motor driver chip, not motor Gnd, which should be 0V.
For the pull-ups try 1k.
Hey so I updated the schematic, please let me know if you have any comments.
 

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sarahMCML

Joined May 11, 2019
370
Hey so I updated the schematic, please let me know if you have any comments.
No, you want your Up and Down buttons to connect to V+, as you originally had them, and your IA and IB inputs to connect to the collectors of the relevant transistors Q1 & Q2, their emitters being grounded as before!

If you measure either collector voltage, when you press the relevant button, it should go from high to low, and the motor should run. The other collector should remain high. Both should be high with no buttons pressed!
 

Thread Starter

John A Bonilla

Joined Mar 11, 2017
92
No, you want your Up and Down buttons to connect to V+, as you originally had them, and your IA and IB inputs to connect to the collectors of the relevant transistors Q1 & Q2, their emitters being grounded as before!

If you measure either collector voltage, when you press the relevant button, it should go from high to low, and the motor should run. The other collector should remain high. Both should be high with no buttons pressed!
Ok, I think I changed what you suggested to fit the circuit. If this isn't what you meant, could you please draw out a diagram of your meaning.
 

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sarahMCML

Joined May 11, 2019
370
Ok, I think I changed what you suggested to fit the circuit. If this isn't what you meant, could you please draw out a diagram of your meaning.
No, keep R5 & R6 connected to +5V, but connect IA & IB to their respective Q1 & Q2 collectors, i.e. to the common point between the collector and R5, for example!
 

Thread Starter

John A Bonilla

Joined Mar 11, 2017
92
No, keep R5 & R6 connected to +5V, but connect IA & IB to their respective Q1 & Q2 collectors, i.e. to the common point between the collector and R5, for example!
I removed R5 and R6 because the point of them was to step the voltage down from 5v to 1.5v for the IR diode so I changed I chose to connect it directly to the AAA battery so that there isn't an extra load on the step-up IC.

Could you draw out what you mean by any chance regarding the common point, I think it would save time? Thanks!
 

sarahMCML

Joined May 11, 2019
370
I removed R5 and R6 because the point of them was to step the voltage down from 5v to 1.5v for the IR diode so I changed I chose to connect it directly to the AAA battery so that there isn't an extra load on the step-up IC.

Could you draw out what you mean by any chance regarding the common point, I think it would save time? Thanks!
No, R5 & R6 go to the +5v supply of the VCC to the motor driver chip, you still need resistors in series with the opto IR diodes of the correct value, otherwise you'll run too much current through them and they'll burn out. They seem to be missing in the last disgram!
It'll take me some time to draw what I mean but I'll be back.
 

sarahMCML

Joined May 11, 2019
370
Ok, here's what I mean. I've drawn all the voltages as if connected to the same 5V supply, but if you wish to run the diode from a lower voltage, don't forget the resistor! Just make sure that it's a suitable value.

L9100P.png

EDIT: Image corrected!
 
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