Help with DC motor driver circuit

Thread Starter

herher

Joined Oct 18, 2011
53
Hi,

Thank you very much for the reply.

One more question here please.

Can I share the ground of the microbox with the ground of the +-15V power supply and motor? Your circuit has showed that they share the common ground but I would like to confirm with you personally once again. And can I know also what is the difference if they didnt share the common ground?

Please advice. Thank you very much.

Best Regards,
herher
 

SgtWookie

Joined Jul 17, 2007
22,221
They must all be connected to a common ground reference.

If they are not, then the circuit won't work, or at least won't work properly. You might damage the opamp due to exceeding its' power rails.
 

Thread Starter

herher

Joined Oct 18, 2011
53
Hi,

Can I test the opa544 on the breadboard?? I am asking this because the distance between the pins are quite small, so the chip actually do not fit nicely on the breadboard. I have to slightly enlarge the distance between pins in order to insert the chip on the breadboard. Is it appropriate to do so?

Please advice. Thank you very much.

Best Regards,
herher
 

SgtWookie

Joined Jul 17, 2007
22,221
The OPA544 is in a 5-lead TO-220 package.

The leads are really too large and spaced too closely for a breadboard.

If you try to force the leads into the breadboard, you will likely ruin that section of the breadboard for future use with jumper wires. Besides, your circuit may try to source/sink current exceeding 1 Ampere; and if so, you may do damage to your breadboard by overheating - too much current for it.

If you "stretch"/bend the leads, you will weaken them.

I don't know if this has been mentioned already, but you MUST use heat sinks on these power opamps, and you MUST use heat sink compound between the tab and the heat sink to transfer the heat. If you don't have heat sinks, you could salvage some from old junked computers. You will have to drill (a) hole(s) to fasten the opamp to the heat sink. If you have a large enough heat sink, you can attach both opamps to the heat sink. IMPORTANT: Note that the tab of the opamp is connected to -V (the negative supply).
 

Thread Starter

herher

Joined Oct 18, 2011
53
Hi,

Thanks a lot for the reply.

Ya, I know I need heatsink, and I already screwed the OPA544 to the heatsink that I have prepared. But now the problem is how am I going to test my circuit since the chip is not appropriate to insert into breadboard. (7805 voltage regulator can be considered as TO-220 chip right? But why the pins distance for this chip is just nice for the insertion on breadboard, while the pin distance for OPA544 is slightly smaller). I think I can't use solder board as well since the holes distance is identical to the breadboard.

I shouldn't use PCB first right since I have not even test the feasibility of the circuit? Then how can i test the circuit?


Please advice. Thank you very much.

Best Regards,
herher
 

SgtWookie

Joined Jul 17, 2007
22,221
Ya, I know I need heatsink, and I already screwed the OPA544 to the heatsink that I have prepared.
OK, that's good.

But now the problem is how am I going to test my circuit since the chip is not appropriate to insert into breadboard.
You should not use a breadboard to test the portion of the circuit that exceeds 1 Ampere current flow, or you will very likely damage the breadboard. You will need to make a circuit board, or very carefully solder wires to the opamp's leads.
7805 voltage regulator can be considered as TO-220 chip right? But why the pins distance for this chip is just nice for the insertion on breadboard, while the pin distance for OPA544 is slightly smaller[/QUOTE]
The 7805's pins are also too large for a breadboard, and you will damage the breadboard by plugging in those big fat leads.

The 7805 is a TO-220 package with the standard 3 leads.
The OPA544 is still a TO-220 package, but has 5 leads. This is really the only way to put an opamp into a TO-220 package, as an opamp requires 5 leads:
1) Noninverting (+) input.
2) Inverting (-) input.
3) +V (positive supply rail; positive supply voltage)
4) -V (negative supply rail; negative supply voltage)
5) Output.

I think I can't use solder board as well since the holes distance is identical to the breadboard.
Typical lead spacing on ICs and many packages such as TO-220 is 0.1" (1/10 of an inch), but on the OPA544 it is 0.05" due to the extra leads required.

I shouldn't use PCB first right since I have not even test the feasibility of the circuit? Then how can i test the circuit?
You will either need to make a circuit board, or you will have to solder wires (as short as possible) to the IC's leads and connect them to the breadboard (only the control signals and GND; the power +v, -v and output must be connected directly to where they need to go, NOT to the breadboard.
 

Thread Starter

herher

Joined Oct 18, 2011
53
Hi,


Thanks again for the reply.

I have tried to run the circuit, I think it can be considered working. As I have tested it with my dc motor, the motor was able to rotate in both clockwise and counter clockwise directions when I supplied positive and negative signals to the input respectively.

However, I am not sure whether the power amplifying function of the chip is functioning as the input signal was generated from a 9V alkaline battery. Hence, the input signal impedance is not that high and the input power is not that low (already enough to drive my motor even without the opamp). So, currently how can I determine whether there is any power amplification from my circuit (the microbox is not with me now).

Besides, I have another question here regarding to the voltage divider. Can I just apply the 15V voltage from the switching power supply and decrease it to my desire voltage (10V) with a miniature potentiometer, and then I will use another multiturn potentiometer (larger size, 10k) to return 0V to 10V analogue voltage back to the microbox? Actually I am a little bit confused with this...will my microbox be effected or damaged if I straight away return this high power signal to it? Ifixit have mentioned before that all load (including microbox) will only use what they need (power) from the power supply right? So, does it mean I can use a high wattage power supply to power up electrical appliance that require lower power as long as the voltage supply to the electrical appliance is within the require range?

Please advice. Please let me know if my explaination is unclear. Thank you very much.


Best Regards,
herher
 
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SgtWookie

Joined Jul 17, 2007
22,221
Hi,


Thanks again for the reply.

I have tried to run the circuit, I think it can be considered working. As I have tested it with my dc motor, the motor was able to rotate in both clockwise and counter clockwise directions when I supplied positive and negative signals to the input respectively.

However, I am not sure whether the power amplifying function of the chip is functioning as the input signal was generated from a 9V alkaline battery. Hence, the input signal impedance is not that high and the input power is not that low (already enough to drive my motor even without the opamp). So, currently how can I determine whether there is any power amplification from my circuit (the microbox is not with me now).
Try using a 1k or 10k resistor in series with the 9v battery to an input.

Besides, I have another question here regarding to the voltage divider. Can I just apply the 15V voltage from the switching power supply and decrease it to my desire voltage (10V) with a miniature potentiometer, and then I will use another multiturn potentiometer (larger size, 10k) to return 0V to 10V analogue voltage back to the microbox?
I don't know what you are talking about.
I thought a couple of 12v or 15v supplies were going to be used for the +V/-V connections for the opamps.


Actually I am a little bit confused with this...will my microbox be effected or damaged if I straight away return this high power signal to it?
I don't know what you are talking about here, either.

Ifixit have mentioned before that all load (including microbox) will only use what they need (power) from the power supply right? So, does it mean I can use a high wattage power supply to power up electrical appliance that require lower power as long as the voltage supply to the electrical appliance is within the require range?
If a microcontroller requires 5v, and your supply is regulated at 5v output, then the microcontroller will only draw as much current as it needs.
 

ifixit

Joined Nov 20, 2008
650
Hi Herher,

I have attached a sketch of how to connect the 10-turn 10K pot and divider to your circuit. The pot can be biased from the +15V supply through 5KΩ resistance (two 10kΩ resistors in parallel). A mini 10K pot set to 5K would do also.

This will put +10V across the 10K 10-turn pot that you require. The motor is mechanically coupled to the pot, so as it turns the voltage on the wiper of the pot will have a voltage of 0 to +10V depending on its position. The wiper connection goes to the "micro box".

I know nothing about your "micro box" so I don't know whether it will tolerate an input of 0 to +10 Volts. Can you supply information on the micro box? A link perhapes?

Regards,
Ifixit
 

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Thread Starter

herher

Joined Oct 18, 2011
53
Hi,


Thank you very much for the replies.

Sgtwookie: I am sorry for my ambiguous explaination...the voltage divider I mean is another circuit that is used to measure the rotation of motor (using multiturn potentiometer). The 10V voltage step down from the switching power supply that I have mentioned is the supply for this potentiometer. In short, the divider circuit will be used as sensor to return the 10V analogue voltage (0V to 10V) back to the microbox. The potentiometer will be connected to the dc motor via shaft and coupling. By the way, I am using two potentiometer for two dc motors.

Ifixit: Thank you very much for the circuit. Actually, I was just troubled by some misconception. But after reading Sgtwookie's and your explaination I think I am clearer now.

Below is the link to the introduction of the microbox I am going to use. Please advice.
http://www.terasoft.com.tw/english/htm/pd-mbox3.html


Bernard: I am using 10 turns, 10k potentiometer. The motor will stop when the measured signal from the potentiometer match to the input being assigned to the PID controller.


What type of wire should I use for my project? I am now still in the testing stage, so I will use normal single core wire, is it safe? Besides, I am going to test my cirucit again by tomorrow or the day after. I will update my progress over here. I hope you all can still continuously assist me and provide your precious opinions. Thank you, thank you and thank you...


Best Regards,
herher
 
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SgtWookie

Joined Jul 17, 2007
22,221
Ahh, OK - no worries.

Your microbox will need to have the same ground as the opamps in order for it to provide the ±10v control signals to the opamp.
 

Thread Starter

herher

Joined Oct 18, 2011
53
Hi,

thanks for the reply.

I have a question over here...will potentiometer spoilt if I accidentally connect its wiper port to the power supply? The supply is around 9V from the alkaline battery...My potentiometer is not funcitoning anymore after I accidentally connect it to the V+. Do you think the potentiometer is spoilt already??

The attached image is the potentiometer I am using.

Please advice. Thank you very much.


Best Regards,
herher
 

Attachments

Last edited:

SgtWookie

Joined Jul 17, 2007
22,221
I don't know WHY you would have done such a thing.

Yes, it is quite possible to destroy a pot if you connect a power supply between one of the ends and the wiper. The problem occurs if the pot is turned to a very low resistance setting from that end terminal to the wiper; current flow increases until the power dissipation in the resistor causes it to burn up.

You should have connected the voltage of the battery across the ends of the pot, and then you get the output voltage level from between the wiper and the negative terminal of the supply.
 

Thread Starter

herher

Joined Oct 18, 2011
53
Hi,

Haih...haha I am sorry. It was an accident. I never use this type of potentiometer (big one) before. I have been using the mini pot as a trimmer. Thus, I thought the position is the same as usually the wiper is at the middle position of the mini pot. Haih...anyway thanks a lot. This is a lesson for me.

Best Regards,
herher
 

SgtWookie

Joined Jul 17, 2007
22,221
Thus, I thought the position is the same as usually the wiper is at the middle position of the mini pot.
The pot you posted not only has a schematic diagram of the parts' connections, it also has a wiper terminal that is colored differently than the end terminals.

If you ever have any doubts about what might be an end and what might be the wiper, it only takes a few moments to verify using a multimeter set to measure Ohms.


If you are turning the pot shaft and the resistance across two of the three terminals does not change, you have found the two end terminals.
 

Bernard

Joined Aug 7, 2008
5,783
Do you have the motors yet? If so have you measured current under load? Also there might be a slight misconseption: rated current should be current at rated load or normal operating current. No-load might be about 100mA, rated current 500mA & locked rotor might be 2A. If there is any spare supply V over motors need, then add some resistance in series with motors, 1 to 2Ω- makes for a softrr start & stop.
Use a soft coupling between pots & motors, rubber tubing etc.
 

Thread Starter

herher

Joined Oct 18, 2011
53
Hi,

Thanks for the reply.

The rated current of my motor is 410mA, but I didnt measure current under actual load. I have tried to operate my system (drive the two motor under actual load) using alkaline 9V battery before. The system is able to operate under the battery supply.

The spare supply you have mentioned is voltage right? If it is voltage, then the supply range I think will not exceed the motor limit. The motor I am using is a 12V DC motor and the voltage range used to drive it is between -10V to +10V.

Please advice. If there is any thing I have misunderstood, please let me know thanks a lot.

Best Regards,
herher
 

Thread Starter

herher

Joined Oct 18, 2011
53
Hi,

What type of wire can i use for my motor connection? Can I use normal single core jumper wire that we usually use on breadboard?

Please advice. Thank you very much.

Best Regards,
herher
 

Bernard

Joined Aug 7, 2008
5,783
I think # 26 should work, that is telephone wire and is what I'm using, short runs only.
Last I herd you were going for +-15V supplys?? 15V - 9V[ alk battery ]= 6V surplus V. 6V/.5A = 12 ohms- so you have from 1 to 12 ohms to play with.
 
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