What kind of servo is this and how do I use it?

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NuclearAwesome
 
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What kind of servo is this and how do I use it?

Post by NuclearAwesome »

Hi! I'm trying to re-purpose the lens extender from a digital camera. Here you can see I've gotten the motor assembly out, and attached my own leads to the terminals. I've got the motor going back and forth (it's a simple 5v dc motor).

What I can't figure out is this servo, and I'd greatly appreciate any insights or help!

I'm going to describe it a bit in case the picture isn't clear: The motor shaft has a wide disc (made of plastic) with gaps, and the disc spins through a slot on the servo. Each side of the servo has two leads, including a common ground. On the outward facing surfaces of the servo there are tiny plastic pieces, one is red and one is white. On the interior surfaces (the 'walls' of the slot) there are very tiny crack-like holes (I think, it's really hard to see).

At first I thought it was an optical servo, with an LED in one side and a photodiode in the the other. To test this, I connected each side in series with a 100 ohm resistor and powered them at 5v, then turned off the lights. I didn't see anything (although it could be emitting in the IR, or maybe the resistance is too high, or possibly I fried the gizmo).

I'd like to be able to use the motor with the servo. Any info would be helpful! Thanks in advance!
Attachments
servo2.png
servo2.png (590.6 KiB) Viewed 1273 times
servo1.png
servo1.png (396.48 KiB) Viewed 1273 times

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adafruit_support_bill
 
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Re: What kind of servo is this and how do I use it?

Post by adafruit_support_bill »

The device with the slot is a photo-interruptor. Some of these use IR. If you can find a part number on it, you might be able to track down a spec sheet.

NuclearAwesome
 
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Re: What kind of servo is this and how do I use it?

Post by NuclearAwesome »

Ok, that's good to know. Alas, no part numbers anywhere... :roll:

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Franklin97355
 
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Re: What kind of servo is this and how do I use it?

Post by Franklin97355 »

The slotted device and the rotor are two parts of an encoder. If the worm gear and its counterpart have a ratio of 100:1 then you would get 200 pulses per revolution from the encoder.

meseta
 
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Re: What kind of servo is this and how do I use it?

Post by meseta »

You could try to see if your camera or webcam can see the IR.

Can you take a photo of the flexible printed circuit that the photointerruptor thing is mounted on? It looks like there are five traces going along the ribbon cable that might be important.

NuclearAwesome
 
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Joined: Mon Sep 19, 2011 2:03 pm

Re: What kind of servo is this and how do I use it?

Post by NuclearAwesome »

Update: I've found a product sheet that has the exact external physical specs of my servo (googling product sheets is sooo much easier when you know what to call a thing--thanks!): http://www.semicon.panasonic.co.jp/ds4/ ... discon.pdf
It's something to go on. Horowitz and Hill has a diagram for exactly that kind of servo, so I'll try that.

@ Mesta: Using the camera to see IR light is a brilliant idea! I'll try it as soon as it gets dark out.

There are indeed five cables coming out of the assembly. One goes to a mutual ground for two pins of the servo, one goes to each of the remaining pins on the servo, and two go to the motor.

Thanks all!

NuclearAwesome
 
Posts: 4
Joined: Mon Sep 19, 2011 2:03 pm

Re: What kind of servo is this and how do I use it?

Post by NuclearAwesome »

Update! I've got it working! That is, I can sense whether something is in the slot or not! Yesss!

I used the diode setting on my multimeter to figure out which side was the LED and which was the photoresistor. Surprise. the 2 leads joined together weren't ground (I foolishly assumed they were ground because they were joined), they go to a higher voltage. My circuit is below. When there's something in the slot, Vout is about 0v, and if nothing is in the slot, Vout is about 1.2v. My response time is lousy, but Horowitz and Hill say I can use a Schmidtt trigger to help with that.

Thanks all! This is very exciting!

(oh, also: The camera trick to see the IR didn't work. Maybe my camera has a filter or maybe it wasn't too bright.)
Attachments
Servo3.png
Servo3.png (30.02 KiB) Viewed 1215 times

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