Calculators with Support of the 82240 IR-Printer

[Martin Hepperle]

(08-06-2014 07:18 PM)Christoph Giesselink Wrote:  

(08-06-2014 08:15 AM)Martin Hepperle Wrote:  

• A logic zero starts with a half bit pause of 854.5/2 = 427.25 us followed by 8 pulses = 8 / 32768 = 244 us followed by a pause of 427.25 – 244 = 183.25 us. The same interval occurs between the bursts of the three start half-bits. This pause corresponds to 183.25/10^6 * 32768 = 6 cycles. This is a critical value as this pause of 6 cycles should be detectable.
  

I confirm. So it's luck that REDEYE receivers work with the TSOP1833 or TSOP4133.

I made a test equipment for a REDEYE compatible printer many years ago. This printer used the TSOP1833 as receiver. The REDEYE transmitter in the test equipment was crystal driven and always send exactly 7 IR pulses in the half bit frame. I cannot remember any problems with the receiver chip in the printer batch production during the lifetime of this product. So we had luck that we always get batches of TSOP1833 that worked with 7 or less pause pulses.

Christoph,

thank you for your reply. I had hoped that you had used some alternative Hardware which I could copy. I think someone mentioned a commercial US product - I would be interested in learning about the innards of this hardware.

If you only sent 7 pulses (which is perfectly within the HP specs of 6-8 pulses) you gained some time for the pause (one 32kHz cycle), which may have helped the TSOP to detect the pause. The HP 48 and 28 seem to send 8 pulses for each burst, resulting in a shorter pause.
Currently I am playing with the 1133, maybe I should try some 1833 instead, if I can get some (I have one 1838, but thought it would be better to move closer to 33 kHz).

Martin