R
Roger Monroe
- Jan 1, 1970
- 0
Hi All,
I'm tasked with logging into a PLC the temperature of a waterbath over time. Well, not exactly. The waterbath has a three character display that shows its temperature. Three 7-segment LED's would show, for example, 45.7
I have a PLC that I have to log what the display shows. I cannot access the back of the display board to pickup any output.
So my idea was to use several phototransistors (I've seen tiny ones) each strategically positioned on a segment of the displayed characters.
I bought two styles from Midwest Surplus (no markings) and tested them with my desk lamp as the light source and it was cool to watch them turn on and off (first time with these things). But when I tested them at the displayof the waterbath they wouldn't turn on.
I tried a waterbath with a green display and one with a red display but none of my phototransistors would work. Digikey lists wavelengths as a parameter in their search engine for phototransistors. How would I know which wavelength to buy and am I even on the right track?
One guy suggested, instead of photodiodes, a webcam run through some OCR software, then the ascii transmitted to the PLC. Now THAT was thinking outside the box. Not really do-able in my situation.
Any suggestions?
All help is appreciated,
Bart
I'm tasked with logging into a PLC the temperature of a waterbath over time. Well, not exactly. The waterbath has a three character display that shows its temperature. Three 7-segment LED's would show, for example, 45.7
I have a PLC that I have to log what the display shows. I cannot access the back of the display board to pickup any output.
So my idea was to use several phototransistors (I've seen tiny ones) each strategically positioned on a segment of the displayed characters.
I bought two styles from Midwest Surplus (no markings) and tested them with my desk lamp as the light source and it was cool to watch them turn on and off (first time with these things). But when I tested them at the displayof the waterbath they wouldn't turn on.
I tried a waterbath with a green display and one with a red display but none of my phototransistors would work. Digikey lists wavelengths as a parameter in their search engine for phototransistors. How would I know which wavelength to buy and am I even on the right track?
One guy suggested, instead of photodiodes, a webcam run through some OCR software, then the ascii transmitted to the PLC. Now THAT was thinking outside the box. Not really do-able in my situation.
Any suggestions?
All help is appreciated,
Bart