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WP34s Repurposing Journey PhotoJournal
02-03-2015, 11:08 AM (This post was last modified: 03-26-2015 10:39 PM by MarkHaysHarris777.)
Post: #18
RE: WP34s Repurposing Journey PhotoJournal
Today I'm adding Tx Rx activity lighting facilitated by the TI LM339N quad open collector comparator chip, and two yellow LEDs which I chose to mount in the upper right-hand corner of the flash-box just to the right of the cradle. I chose to monitor both lines (Tx, Rx), and each line uses 1/4 LM339. The theory is really simple, each comparator is given a reference voltage from a resistor based voltage divider (on the inverting input of the amp) and the non inverting input is then 'compared' to the reference voltage. If the line (active state low) drops below 2.5v, then the led glows. The current limiting resistors were chosen deliberately high (even though it means dimmer LEDs) to keep the current drain lower.

The Tx Rx LED circuits are based on the following schematic:

[Image: schematic3.jpg]

In addition to the LM339N (and Tx Rx LEDs) I also added the power switch (DPDT 5.1v & 3.4v) and insulated the connections:

[Image: lm339-3-2.jpg]

The following two pics give alternate elevations of the new components. I had to move the 3.4v distribution lines to the back side of the Manhattan board.

[Image: lm339-1-2.jpg]

In this final pic of the LM339 from the right end you can see the mounting for the Tx Rx LEDs, and the 100 mf cap which I decided today to place on the 3.4v line from the FTDI /

[Image: lm339-4-2.jpg]


Kind regards,
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RE: WP34s Repurposing Journey PhotoJournal - MarkHaysHarris777 - 02-03-2015 11:08 AM

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