DM42: IR-receiver photodiode specs?

Discussion around the Swiss Micros DM42 calculator.
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mcc
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DM42: IR-receiver photodiode specs?

Post by mcc » Fri Oct 02, 2020 6:56 am

Hi,

Out of curiosity I want to build a IR-receiver with a microcontroller.
"Unfortunately" there a different IR-receiver phtodiodes available for different
parts of the IR-spectrum.

What IR-photodiode I need to buy?

Thanks a lot for any help in advance! :)

Cheers!
mcc
DM 42 - SN: 00373, Firmware release v.:3.16. / DMCP 3.20. as compiled by SwissMicros

grsbanks
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Re: DM42: IR-receiver photodiode specs?

Post by grsbanks » Fri Oct 02, 2020 10:23 am

The printer's technical documentation says:
The optimum optical wavelength for the printer is 940 nanometers (nm), but wavelengths as short as 850 nm and as long as 1000 nm can be used with only minor reductions in the distance over which data can be sent to the printer.
Presumably the diode is matched to that area of the spectrum.

Just make sure you don't get a receive unit that integrates the pulses. The timing of the Red-Eye protocol is pretty critical.
There are only 10 kinds of people in the world: those who understand binary and those who do not.

mcc
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Re: DM42: IR-receiver photodiode specs?

Post by mcc » Fri Oct 02, 2020 12:48 pm

Hi grsbanks,

thanks for your help!

...is the wavelength of the transmitter diode known, which is used for the DM42 ?

Cheers!
mcc
DM 42 - SN: 00373, Firmware release v.:3.16. / DMCP 3.20. as compiled by SwissMicros

grsbanks
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Re: DM42: IR-receiver photodiode specs?

Post by grsbanks » Fri Oct 02, 2020 1:23 pm

mcc wrote:
Fri Oct 02, 2020 12:48 pm
...is the wavelength of the transmitter diode known, which is used for the DM42 ?
I don't remember exactly which diode was chosen. I used to have its datasheet somewhere but can't lay my hands on it right now. What I can say is that the diode was chosen to match the characteristics of the 82240A/B printer, so if you look for a photodiode tuned to that same 850-1000 nm range, you should be good.
There are only 10 kinds of people in the world: those who understand binary and those who do not.

MeinKuipers
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Re: DM42: IR-receiver photodiode specs?

Post by MeinKuipers » Fri Oct 02, 2020 1:28 pm

There is a Technical Intefacing Guide for the 82240B IR printer (downloadable here: https://www.hpcalc.org/details/4742) which has all the gory details and specifies the 940 nm as quoted earlier.
From my own experience I can confirm that the IR frequency is uncritical, but the modulation frequency and burst size is tricky, so most generic demodulating IR receivers may seem to work but have a too long recovery time and will quickly garble the data. So the Arduino will have to do the demodulation (it is very capable to do so). I have not used a real printer but rather a PC with a printer emulator and it is a really nice addition to my DM41X (and works with the DM42 as well although I have not tested that myself).
Regards from NL,
Meindert Kuipers DM41X #48

dk-
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Re: DM42: IR-receiver photodiode specs?

Post by dk- » Fri Oct 02, 2020 1:33 pm

Regarding the pulses: When I built my homemade printer I used an IR transistor that had fairly slow fall and rise times (something around 15us for 90% <-> 10% transitions), almost on the edge of detecting the 32768Hz carrier frequency. But keep in mind that it's entirely up to you if you want to detect this carrier. The protocol is perfectly decodable even if you don't receive the individual pulses. If the signal is instead rectified and smoothed either through purposeful circuit design, or due to side effects from imperfect components, you might not get the same range and discrimination from other IR sources, but it will still work well.

mcc
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Re: DM42: IR-receiver photodiode specs?

Post by mcc » Fri Oct 02, 2020 6:55 pm

Hi,

oh YEAH! :)
Great informations - thanks a lot!
Despite the fact that I know photoTRANSISTORS...I didn't have thought of them in this context...nice
to be reminded of something which was forgotten to be known. ;)

Cheers!
mcc
DM 42 - SN: 00373, Firmware release v.:3.16. / DMCP 3.20. as compiled by SwissMicros

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