Jeremy Leach
Senior Member
This is PICAXE-related as it feeds my PICAXE (!), so here goes ...
I'm having some difficulty getting my photo-reflector to work on my encoded disc and I'm just wondering if anyone else has had any experience. I'd appreciate any advice.
The one I'm using is an SY-CR102 from Maplin <A href='http://www.maplin.co.uk/module.aspx?TabID=1&ModuleNo=12709&doy=search' Target=_Blank>External Web Link</a>
Unfortunately it doesn't have a datasheet, the diagram is difficult to understand and I can't find one on the net, except for one in chinese, which I can't open.
I've gone by the example this guy used <A href='http://www.jeffree.co.uk/Pages/speedmeasurement.html' Target=_Blank>External Web Link</a> and have this circuit:
<code><pre><font size=2 face='Courier'>
+5V o------------------o----------------o
| |
.-. .-.
| | | |
220R | | | | 10K
'-' '-'
| |
| |
| o-------------o Output
| |
| |
.----------------------------------.
SY-CR102 | | | |
Opto-reflector | IR | |/ |
| LED V -> -| Phototransistor |
| - |> |
| | | |
| | | |
| | | |
'----------------------------------'
| |
GND o-----o------------o----------------o
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
</font></pre></code>
I've made a disc that is coloured in black marker pen with aluminium foil stuck over in the desired encoded pattern. The opto sensor is 1mm from the surface of the disc as per the maplin details.
The trouble is, I'm getting a voltage of 0.16Volts for the foil and only 0.19Volts for the black areas. I'm not sure why but there seems to be a few possibilities:
1. Photo transistor series resistor too high?? Although I'd still think there would be a fair swing of voltage.
2. My 'black' marker pen marks, although they look black may be as relflective as the foil ??
3. The other possibility is that this isn't the right circuit to use. The Maplin diagram hints at an emmiter-follower type arrangement:
<code><pre><font size=2 face='Courier'>
+5V o------o----------------o
|
|
|
|
|/
-| Photo transistor
|>
|
|
o------------o Output
|
.-.
| |
| |
'-'
|
GND o--------o-----------------o
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
</font></pre></code>
and I've read a brief statement in another electronics book that this arrangement will give faster photo transistor response - although I'm not clear why.
Anyone got any tips?
PS: Oh and I made the fatal mistake of not breadboarding this first, thinking it's bound to work - so I'm just asking for tips before brandishing my soldering iron ;-)
Edited by - Jeremy Leach on 20/08/2006 17:26:44
I'm having some difficulty getting my photo-reflector to work on my encoded disc and I'm just wondering if anyone else has had any experience. I'd appreciate any advice.
The one I'm using is an SY-CR102 from Maplin <A href='http://www.maplin.co.uk/module.aspx?TabID=1&ModuleNo=12709&doy=search' Target=_Blank>External Web Link</a>
Unfortunately it doesn't have a datasheet, the diagram is difficult to understand and I can't find one on the net, except for one in chinese, which I can't open.
I've gone by the example this guy used <A href='http://www.jeffree.co.uk/Pages/speedmeasurement.html' Target=_Blank>External Web Link</a> and have this circuit:
<code><pre><font size=2 face='Courier'>
+5V o------------------o----------------o
| |
.-. .-.
| | | |
220R | | | | 10K
'-' '-'
| |
| |
| o-------------o Output
| |
| |
.----------------------------------.
SY-CR102 | | | |
Opto-reflector | IR | |/ |
| LED V -> -| Phototransistor |
| - |> |
| | | |
| | | |
| | | |
'----------------------------------'
| |
GND o-----o------------o----------------o
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
</font></pre></code>
I've made a disc that is coloured in black marker pen with aluminium foil stuck over in the desired encoded pattern. The opto sensor is 1mm from the surface of the disc as per the maplin details.
The trouble is, I'm getting a voltage of 0.16Volts for the foil and only 0.19Volts for the black areas. I'm not sure why but there seems to be a few possibilities:
1. Photo transistor series resistor too high?? Although I'd still think there would be a fair swing of voltage.
2. My 'black' marker pen marks, although they look black may be as relflective as the foil ??
3. The other possibility is that this isn't the right circuit to use. The Maplin diagram hints at an emmiter-follower type arrangement:
<code><pre><font size=2 face='Courier'>
+5V o------o----------------o
|
|
|
|
|/
-| Photo transistor
|>
|
|
o------------o Output
|
.-.
| |
| |
'-'
|
GND o--------o-----------------o
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
</font></pre></code>
and I've read a brief statement in another electronics book that this arrangement will give faster photo transistor response - although I'm not clear why.
Anyone got any tips?
PS: Oh and I made the fatal mistake of not breadboarding this first, thinking it's bound to work - so I'm just asking for tips before brandishing my soldering iron ;-)
Edited by - Jeremy Leach on 20/08/2006 17:26:44