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Step 3Base resistors
I used 10k base resistors. Solder where circled. I messed up the pnp transistor in this pic. Disregard the whited out area.
**EDIT: the base resistor for the "data in" tranny should be 22k. Also, data out tranny should not be pulled up with the 10k resistor network. Instead, pull it up with a 1k resistor. I just realized that these two resistors will form a voltage divider, and if each is 10k data high will be 2.5V... no good. (Alternatively, you could just leave things the way they are, but connect Data Out transistor's collector to all remaining 5 10k pullups. This makes the divider 2/10, which should still suffice. On my particular circuit, that's what I did, and it registers 4.24V as high, which should be enough.)
Picture 2:
The pnp transistor gets two base resistors wired as a divider. Solder the 10k resistor between emitter and base. Solder one end of your 5k (actually I used 3.3k cuz I had it lying around) to the base. You can connect collector to Vpp pin, now, since it is close.
Eventually, you will be connecting the emitter to 12.5V source. The 10k resistor keeps the base high - thus programming voltage off. When pin 5 of your parallel port goes low, it pulls the base low, via the 5k resistor.
The schemmy I used also showed a 10k resistor between collector and ground. I'm not sure what it's for. I think it is to ensure that the PIC's MCLR pin does not float. But that would be silly, since MCLR is usually going to be connected to an external pullup, anyway. In addition, MCLR pin is an active sink of a few microamps. It doesn't float. At any rate, I have recklessly omitted this resistor. Bonus points for anyone who can tell me why this is bad idea.
**EDIT: the base resistor for the "data in" tranny should be 22k. Also, data out tranny should not be pulled up with the 10k resistor network. Instead, pull it up with a 1k resistor. I just realized that these two resistors will form a voltage divider, and if each is 10k data high will be 2.5V... no good. (Alternatively, you could just leave things the way they are, but connect Data Out transistor's collector to all remaining 5 10k pullups. This makes the divider 2/10, which should still suffice. On my particular circuit, that's what I did, and it registers 4.24V as high, which should be enough.)
Picture 2:
The pnp transistor gets two base resistors wired as a divider. Solder the 10k resistor between emitter and base. Solder one end of your 5k (actually I used 3.3k cuz I had it lying around) to the base. You can connect collector to Vpp pin, now, since it is close.
Eventually, you will be connecting the emitter to 12.5V source. The 10k resistor keeps the base high - thus programming voltage off. When pin 5 of your parallel port goes low, it pulls the base low, via the 5k resistor.
The schemmy I used also showed a 10k resistor between collector and ground. I'm not sure what it's for. I think it is to ensure that the PIC's MCLR pin does not float. But that would be silly, since MCLR is usually going to be connected to an external pullup, anyway. In addition, MCLR pin is an active sink of a few microamps. It doesn't float. At any rate, I have recklessly omitted this resistor. Bonus points for anyone who can tell me why this is bad idea.
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