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Step 4Construction - the PCB
This is pretty straightforward. Just a double sided PCB with some SMD components on the top. Sorry if you're a through hole person, but it's a lot easier to make SMD projects....less holes to drill. You should have a steady hand, a temperature controlled soldering station and plenty of light and magnification to make things easier.
The only thing of note in the construction of the PCB is the inclusion of a connector for programming the PIC. This connects to the ICSP pins on the PIC and you'll need an ICSP programmer. Again I used a handy to my junkbox connector. You can omit this and just solder wires to the pads if you like.
Alternatively if you only have a socketed programmer, you can make a header that plugs into your socket and then solder that to the ICSP pads. If you do this, then disconnect Rx and connect Ry which are just zero ohm links (I just use a solder blob). This will disconnect the rest of the circuit power from the PIC so it doesn't interfere with the programming. A socketed programmer just uses the ICSP pins like a ICSP programmer, there is no magic involved really.
You also need to do this if by mistake you've forgotten to put a delay in the code before the RTC starts up. For the 16F88 the ICSP programming pins are the same as the pins needed for the 32.768kHz crystal used for the RTC......if the T1 external oscillator (ie the RTC) is running before the ICSP can start it's work, then the programming will fail. Normally if there is a reset on the MCLR pin and there is a delay, then ICSP data can be sent to these pins and programming can start properly.
However by isolating the power to the PIC the ICSP programmer (or socketed programmer with a header) can control power to the device and force a program.
The other things to note are that the crystal pads on the PCB were originally designed for SMD crystals. I couldn't wait for some to be delivered so the 32.768kHz watch crystal was soldered to the top as shown, and the 20MHz crystal was attached by drilling a couple of holesin the pads, poking the crystal in through the bottom and soldering onto the top. You can see the pins just to the right of the PIC16F88.
The only thing of note in the construction of the PCB is the inclusion of a connector for programming the PIC. This connects to the ICSP pins on the PIC and you'll need an ICSP programmer. Again I used a handy to my junkbox connector. You can omit this and just solder wires to the pads if you like.
Alternatively if you only have a socketed programmer, you can make a header that plugs into your socket and then solder that to the ICSP pads. If you do this, then disconnect Rx and connect Ry which are just zero ohm links (I just use a solder blob). This will disconnect the rest of the circuit power from the PIC so it doesn't interfere with the programming. A socketed programmer just uses the ICSP pins like a ICSP programmer, there is no magic involved really.
You also need to do this if by mistake you've forgotten to put a delay in the code before the RTC starts up. For the 16F88 the ICSP programming pins are the same as the pins needed for the 32.768kHz crystal used for the RTC......if the T1 external oscillator (ie the RTC) is running before the ICSP can start it's work, then the programming will fail. Normally if there is a reset on the MCLR pin and there is a delay, then ICSP data can be sent to these pins and programming can start properly.
However by isolating the power to the PIC the ICSP programmer (or socketed programmer with a header) can control power to the device and force a program.
The other things to note are that the crystal pads on the PCB were originally designed for SMD crystals. I couldn't wait for some to be delivered so the 32.768kHz watch crystal was soldered to the top as shown, and the 20MHz crystal was attached by drilling a couple of holesin the pads, poking the crystal in through the bottom and soldering onto the top. You can see the pins just to the right of the PIC16F88.
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