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WP34s Repurposing Journey PhotoJournal
02-05-2015, 12:26 PM (This post was last modified: 02-22-2015 12:35 AM by MarkHaysHarris777.)
Post: #25
RE: WP34s Repurposing Journey PhotoJournal
With the exception of the mA meter (3v Icc), the electronics of the Flash-box 1.0 is complete, and I have successfully updated my WP34s with calc_xtal_full.bin (albeit a back-level version). The last addition to the Manhattan board are the voltage monitors; amp (4) monitors the 3v line source and raises a red LED indicator warning should the voltage drop below 2.8 volts, while amp (3) monitors the voltage of the J32 reset pin on the wp34s-side of the J32 reset-ground-shot-diode. This is perhaps the real beauty of this particular project; because the wp34s gives no indication that it is 'on' and running during the 'erase' or 'update' process amp (3) monitors the reset line which goes 'high' when the calculator is 'on'. The voltage monitors are based on the following schematic:

[Image: voltmon_schema.jpg]

Each of the four comparators works the same way (high gain op amp without feedback resistor, and open collector) in that the Q out transistor turns on (allowing LED to glow) should the non inverting input (+) drop below the inverting input (-). In the case of the 3v monitor the reference voltage is placed on (-) and if the line voltage drops below 2.8 volts the red LED glows. On the other hand, the reference is placed on (+) on amp (3). If the reset J32 pin raises above the reference then the wp34s is 'on' and the green power diode glows.

... one last look before we button it up ...

[Image: fb_back1.png]

The following pic shows the completed Flash-box in the update mode with the power applied and the WP34s 'ON'. The only design plan not yet implemented is the mA meter (which is on the way... snail mail... )

[Image: calc_on.png]

The yellow LEDs in the upper right monitor the Rx Tx signals (dim rapid flicker, better than nothing) and the red LED in the lower right (normally off) signals a problem with the 3v line. There are actually two warnings that will occur should the 3v line have a problem... because the reset pin J32 will NOT raise high enough for the LM339 to turn on the LED unless the 3v line is above 2.8 volts (so we should have plenty of warning before beginning the flash).

During the power-on, erase, reset sequence the three green LEDs makes it very easy to remember where one is in the sequence (which otherwise is somewhat confusing).

Voila. ... and of course,

Kind regards,
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RE: WP34s Repurposing Journey PhotoJournal - MarkHaysHarris777 - 02-05-2015 12:26 PM

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