6 replies to this topic

[Inquisitor]

Before starting to dissect the InkJet InkJet Dissection I was just “SURE” that there would be 2 stepper motors inside… one for the moving the paper in and out and the second for moving the printer cartridge back and forth across the paper. Once splayed across the floor, I found there was a stepper motor for the paper, but there was just a cheap looking DC motor (although rather stout) for driving the cartridges. It uses a timing belt type pulley system, but also had a strange piece of smoked colored plastic stretched across the cartridge path. At first I had no clue how this worked… it didn’t have any printing on it and it didn’t look magnetic. It wasn’t till I took a close up picture of it for this post that I noticed the smoked color was actually fine lines! (Damn old eyes) Wa’la! It’s just an optical interrupter. I can use this with the Netduino.

BUT… alas no. It has 6 connectors to it instead of the 4 I’m used to. Does anyone have an idea what this thing is called so I can Google it?

Also, do you know if it’s possible to get this etched strip in a roll… say 100 feet?

Thanks All

[CW2]

BUT… alas no. It has 6 connectors to it instead of the 4 I’m used to. Does anyone have an idea what this thing is called so I can Google it?

I believe it is called 'raster' or 'encoder strip', you can get it for cheap at eBay. Regarding the number of pins on the connector, it would help to see the back side of the sensor module - it may be just extra not-connected pins, or for example the encoder sensor may have two sensing elements to determine the direction of the movement, or to increase precision etc.

[Inquisitor]

I believe it is called 'raster' or 'encoder strip', you can get it for cheap at eBay. Regarding the number of pins on the connector, it would help to see the back side of the sensor module - it may be just extra not-connected pins, or for example the encoder sensor may have two sensing elements to determine the direction of the movement, or to increase precision etc.

Thanks CW2. That was the phrase I needed. 'encoder strip' Unfortunately, the strip material is rather expensive. I just imagined it being made on huge rolls for the InkJet industry... not being $89 for 10 feet. But here is the backside of the circuit board in case someone else wants to mess with it. I also found this article that might be of help.

Messing with an Encoder

But it spawned another idea, I'll put into another topic.

[Mike P]

 2011-09-05_2058.jpg   27.79KB   16 downloads This would be my guess.(see labels on photo) The GND plane is pretty obvious - large filled area. There is a cap between GND and what I would assume is VCC VCC is also supplied to one pin of the sensor via a resistor. This would be a current limiting resistor for the LED side of the light gate. The detctor side appears to have a connection to VCC and GND and two ouptuts. These are normally called A and B and are 90° out of phase. This allows you to work out which direction the sensor is moving. If you think of the output as a 2-bit binaty value then the signal would 0-1-3-2 going in one direction and 2-3-1-0 in the other direction.

[Inquisitor]

 2011-09-05_2058.jpg   27.79KB   16 downloads
This would be my guess.(see labels on photo)
The GND plane is pretty obvious - large filled area.
There is a cap between GND and what I would assume is VCC
VCC is also supplied to one pin of the sensor via a resistor. This would be a current limiting resistor for the LED side of the light gate.
The detctor side appears to have a connection to VCC and GND and two ouptuts. These are normally called A and B and are 90° out of phase. This allows you to work out which direction the sensor is moving.
If you think of the output as a 2-bit binaty value then the signal would 0-1-3-2 going in one direction and 2-3-1-0 in the other direction.

Mike P,

Thank you for the reply. Most of this fits in with what I’ve learned so far having started with the Sparkfun’s tutorial. It brings up a couple of questions if you or someone could help. I think the first thing that gets me second-guessing what I’m seeing is the additional stuff. In this case…

• there are two connectors with a total of 9 pins and I know no manufacturing engineer is going to let a high volume piece go out with things that aren’t needed.
• No capacitor was needed in the Sparkfun tutorial. All I know (so far) is… capacitors can store electricity and they act as some kind of filter for AC. What does it do in this circuit (just the technique name… I can look it up)?
• Taking a WAG… is this what’s called a “bandwidth filter”? And if so… what or why would we want to filter anything out of the signal?

Thanks for your help

BTW – What are you doing to insert the thumbnail?

[CW2]

• there are two connectors with a total of 9 pins and I know no manufacturing engineer is going to let a high volume piece go out with things that aren’t needed.
• No capacitor was needed in the Sparkfun tutorial. All I know (so far) is… capacitors can store electricity and they act as some kind of filter for AC.

In the tutorial you linked in your second post, there is a picture of almost the same sensor board (in the middle of the page, just above the sensor schematic) and the second (small) connector is described as "connector to paper sensor". A few lines below there is a photo of the back side of the board with colored traces, which are very similar to your board (I think only sensor outputs A and B are wired a little bit differently). The capacitor between ground and power supply is usually called decoupling capacitor.

[Mike P]

This would be a guess but there was probably another sensor conected to that 3 pin connector. Maybe a home position sensor or something.
The decoupling cap serves to smooth out the power supply. It acts like a shock absorber on the supply voltage. Without it small spikes on the power supply would be created whenever loads were switched on and off and these spikes might be transfered to the output signal.
The spikes on the output could be mistaken for real output transitions and cause the encoder to lose its count.

I posted some code on the Wiki last night for a rotary encoder. Chances are that it would work fine with your strip as well.
http://wiki.netduino...oder-Input.ashx