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My purpose is to build a cheap quick-and-dirty "robot" using 2 electrical screwdrivers connected to the wheels and a smartphone to control them. I want to control each motor (forward/idle/reverse) using two phototransistors/photodiodes/photoresistor facing the smartphone screen.

My idea is to use the battery (3.6V) and motor of this electrical screwdriver http://www.ikea.com/us/en/catalog/products/60196103/ and somehow connect it to a smartphone screen to move it forward or backward or switch it off. The smartphone would show two squares on the screen each of them can be black or white. The phototransistors would be placed on the screen, detect the color and switch the motor (using other transistors or relays). For example if both squares are white the motor would go forward, if both are black backwards and if one is white and the other black the motor would be idle (without short-circuiting the battery).

I am not an electronics expert and I don't know what is a good detector for the light coming from a smartphone screen (infrared detectors won't work). I assume that the detector should be touching the screen and isolated from exterior light. I don't know which is a good switch for this kind of motor (3.6V), either a transistor or a relay.

I would like the solution to be simple and cheap, using the 3.6V battery of the motor. I want the motors to be either on or off depending on a light threshold (no linear response depending on the light).

UPDATE: This is the motor Motor Ikea Fixa 3.6V

When running without load (only the gears) the current I measured is 1.84A, but when it starts is higher (I think I saw more than 3A).

I found this specs that may be from the same motor: http://www.mabuchi-motor.co.jp/cgi-bin/catalog/e_catalog.cgi?CAT_ID=rs_380sh the name is nearly the same (there's an extra H) and the dimensions are the same.

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  • \$\begingroup\$ What current do the motors consume from the battery. How much noise is back-injected onto the battery when the motor is running? \$\endgroup\$ – Andy aka Mar 12 '14 at 11:01
  • \$\begingroup\$ I don't know. I don't have bought the screwdriver yet. I only have the "specs" from the Ikea page. Sorry. Here blogouillage.net/2013/05/diy-cat-feeder-v20.html there's a picture of it disassembled. \$\endgroup\$ – user2518618 Mar 12 '14 at 11:14
  • \$\begingroup\$ You need to find this info dude. \$\endgroup\$ – Andy aka Mar 12 '14 at 11:18
  • \$\begingroup\$ I will buy it in a few days. Can I measure the noise with a tester? Is it the voltage drop when it is running? \$\endgroup\$ – user2518618 Mar 12 '14 at 12:17
  • \$\begingroup\$ You'll need an oscilloscope to measure the noise. \$\endgroup\$ – Andy aka Mar 12 '14 at 12:26
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I think that your project can be done very easily. 1)because you don't have an electronic background, I will tell you to ignore the comments about noise being injected into the battery. 2) you are right about the screwdriver motor. It does give you more torque...considering that we don't know anything about your load, you might need it. 3) Those screwdrivers usually have a rechargeable battery and wall charger. If you have the one that came with the screwdriver, really ignore the noise comment. 4) Do you know what a relay is? From digikey.com you buy a relay for your project. I will suggest that you buy a relay that can handle at least 5volts at 5A max. 5) your motor will be connected to your relay. You will activate the relay with the output of a color sensor. There many color sensors out there. I do believe that there is a color sensor that gives you a 5v output when a black black line is detected. Check parallax.com or sparkfun or robotshop.com. 6) To recap, when the sensor sees black on the screen, the output will go high, hence activating your relay, which will turn on your motor. Good luck !

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  • \$\begingroup\$ Thanks for all links. The screwdriver has charger and lithium battery. I am thinking of implementing an H bridge using 2 SPDT relays as shown at the bottom of this page thebox.myzen.co.uk/Workshop/Motors_1.html. I don't know if I need to use transistors or there are color sensors that can be connected directly. Do you recommend using a separate 5V battery for the sensors? (Because of the noise and the fact that the screwdriver battery is 3.6V) \$\endgroup\$ – user2518618 Mar 18 '14 at 6:07
  • \$\begingroup\$ The h-bridge will be perfect for your application. If the sensor is using 5v, then yes you will need a separate voltage source. \$\endgroup\$ – RalphGJr Mar 18 '14 at 11:28

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