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PICPROTO 8/14, 18/20 and 28/40 PIC prototyping boards
Description...
These boards offer a quick way to check out the capabilities of various Arizona Microchip Inc. ‘PIC’ microcontrollers. They are all Plated-through-Hole (PTH) boards which are rugged enough to be used for final ‘one-off’ designs, if needed. Each unit has a resistor-programmed linear power supply letting the user try a design at various supply voltages. A shuttered standard phone-jack connection is fitted so that the unit will plug into an ICD2 programmer/ debugger from the get-go. The power supply has reverse polarity protection and uses an industry standard 2 pin header to connect to a ‘wall wart’ 9VDC unregulated mains adaptor. All units have provision for adding Microchip’s range of 8 pin IIC EEPROMs from small (24C01) to large (24LC65A) etc. All units have a power-on LED to help you avoid that....’why is it not working?’....’oops, maybe it would work better with the power on!’ moment. A small reset button is provided (don’t use it or don’t fit it for PICs with internal reset). We thought about fitting a USB jack to the higher-end units...but you can add this quite simply yourself if needed (it’s only 4 wires!). All units have a ‘clock’ area capable of accepting crystal, resonator (with or without internal caps) or allowing use of the clock lines for other things (for PICs with internal clock capability). For high frequency or sensitive clocks, the external connects have deliberately been routed through via holes on the PCB.. so gently drill them to break the connection to the extra tracking. Supply decoupling capacitors are fitted, but should obviously be extended depending on what you fit to the prototyping area. The prototype area can be easily documented by designing on a photocopy of the basic artwork. Reference to circuit points is made easy using the X/Y letter/number grid marked on the board. All relevant PIC connections are brought to a 0.1” pitch row to the right of the prototyping area, which is pre-routed with Vcc and Vss rails. The board corners have standard nylon pillar positions. We recommend you use the ‘RICHCO’ types with locking ‘ears’.
Differences between the boards.....
PICPROTO 8/14...
This has provision for 6 LEDs (we thought about adding switches too...but that’s easy enough to do on the prototype area).
PICPROTO 18/20...
Has a simple RS232 interface with transmit and receive, but no hardware handshake (not normally a problem). It is an ‘energy stealing’ design which derives a negative transmit level from the incoming receive line. It is therefore limited to half-duplex operation. For the less capable PICs, a ‘bit bashing’ firmware RS232 solution may be coded...more powerful chips have RS232 as standard. The lines are not tracked to the PIC, so you could even add pins committed to a ‘bit basher’ RS232 to a PIC design with another (built-in) RS232. A voltage reference and op-amp scaling area is provided for PICs with an external AVss/ AVdd feature. If this feature is not needed, you could ‘hack and bash’ the board to use the op-amp for other things.
PICPROTO 28/40...
Also has the op-amp and the RS232 circuit. It also has provision for a standard alphanumeric LCD display drive. We deliberately did not fit this to the board because a) you may have one lurking in your ‘junk box’ b) you might not need one at all c) They are available in such a wide variety of shapes, sizes and capabilities. A contrast pot is fitted.
Assuming R5=240R (R4 on 18/20 and 28/40 boards)........ the values below were measured from a working unit....
Selection of resistor R6 (R5 on 18/20 and 28/40 boards)........
Value Vss Value Vss Value Vss
820R 5.51 430R 3.50 200R 2.29
750R 5.20 390R 3.28 180R 2.18
680R 4.79 390R 3.28 160R 2.07
620R 4.48 330R 2.95 150R 2.02
600R 4.36 300R 2.81
560R 4.14 270R 2.65
510R 3.91 240R 2.50
470R 3.69 220R 2.38
A standard built unit is shipped with a 750R resistor to provide Vss=+5VDC nominal (with a +200mV overhead to allow for loading).
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