Using ULN2008 to control 4 motors

kenwtn

HI All,
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I have a robotic arm that has four motors controlling the different movements. I really can't tell you too much about how the motors are wired since I do not have schematic. This is what I do know is running from the robotic arm to the motion controller are 8 wires. I have tested the wires and found that 2-wires is not connected to anything, then 4-wires one connected to each motor, and then the remaining two wires control direction of each of the motors. It appears that the two wires simply reverse the polarity to the motor. When I touch one of the control wires to a motor wire the motor goes one direction and then when I touch the other control wire to the same motor wire the motor runs in the reverse direction.
·· OK, my basic stamp has its own power source and the robotic arm has its own source of power. Is it possible to use the UNL2008 to control these motors? If so can anyone show me a diagram of how to do this?
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Thanks In Advance

LoopyByteloose

I read your information, but it seem a bit muddled.

You need to determine if you have conventional DC motors or Stepper motors.

The UNL2008 will control some stepper motors and change direction. It has only 7 circuits, so it cannot be used for two motors [noparse][[/noparse]you would need the UNL2308 with 8 circuits]. It is also limited to 500ma total. Any more and it will self-destruct.· So you need to measure the resistance of each motor and calculate the current draw.

For conventional DC motors to change direction, you require an H-bridge.

I have difficulty following your count and descriptions of the number of wires and how change of direction is achieved. Obviously when you say two wires are connected to nothing, that seems highly unlikely. They would at least be chassis ground shielding. All wires need to be accounted for in order to really achieve anything reliable. There is the possiblity that diodes are being used and some wires would read 'dead' or unconnected in one direction of polarity, but would actually show a connection when the polarity is reversed

AS I read you....
4 wires go to one motor each. 2 wires go to all 4 motors, but cause a change in direction when power is shifted from one to the other. 2 wires are connected to nothing.

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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

kenwtn

The circuit seems simple I think I did a poor job of describing it. Another mistake I made was the chip is the UNL2308 I did buy the 8 chanel VS the 7. It appears they used a 8 line ribbon cable for whatever reason, but I can see and meter those two lines that I say are dead. The 8 line ribbon cable runs from the control box to the base of the robotic arm where the battaries are located. Those two wires simply deadend there. Ok, now the other wires 4 wires I know go one each to the four motors and the other two which I called control wires are power wires one is + and the - . When I meter from the + to anyone of the motor wires I read +2.5V when I meter from the other control wire - I read -2.5V. When I meter between the two control wires I read +5V. Inside the battery box there are 4 D batteries which account for the 5V. It seems they have split them and use 2.5V to drive the motors. Inside the control box is simple enough there is a rocker switch for each motor. One motor wire runs to each switch and the contol wires +2.5V to one side of the switch and -2.5V to the other side. When you push the switch up it makes the motor rotate one direction and when you pull the switch down it rotates the motor in the other direction. When the switch is centered the motor is off.

I hope this helps better explain what I have.

Jon Williams

The ULN only sinks current so I don't think you can use it in your application to change motor direction.

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Jon Williams
Applications Engineer, Parallax

kenwtn

Ok, I thought it could be used as a switch? Nut and Volts Electronic Control For DC Motors.

Jon Williams

You can, but it only sinks current (provides ground to your circuit) -- to change motor direction you have to change the direction of current through it. If you want you motors to run in one direction, the ULN is great; for applications where direction must be changed you need an h-bridge. Another component you might want to look into is the L293D -- it can sink and source current from its outputs and is useful in this type of application.

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Jon Williams
Applications Engineer, Parallax

kenwtn

Thanks Much for your help and Ideas I will look into those options.

LoopyByteloose

Since it is a ribbon cable [noparse][[/noparse]they don't make 6 wire ribbon], it could be possible to have two wires not connected.

But 8 wire ribbon cable isn't that common either. The standard connectors go down to 10 wires.

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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan