picXplorer20
The 20pin PIC motherboard is labelled picXplorer20. The programming socket can be used to programme most of the popular PIC systems used in education. Users wishing to write code in assembler or C can still use this motherboard but PICs must be programmed first before plugging into the PIC socket. NOTE: Code written in C or assembler will need to take account of how the input and output connections are wired up. More flexibility is provided by picXplorer08 where the data direction can be switched using a DIL switch.
Input modules must be plugged into the left hand connectors, output modules must be plugged into the right hand connectors. A few output modules e.g. the MOSFET driver, can utilise a higher voltage power supply to drive high power devices. In which case, they should be plugged into either Q0 or Q1. The jumper links at Q0 and Q1 must then be set to +V to use the higher voltage supply.
picXplorer20 motherboard
Circuit diagrams
Details of the programming connector
Output connections
Input connections
Power supply
picXplorer can be powered either by a 6V battery connected to PL2 or a smoothed dc power supply connected to PL1. The centre pin of PL1 is the positive connection. The battery is automatically switched off when a dc power connector is plugged in. If the polarity of either the dc power connector of the battery is inadvertently reversed then no damage will occur due to polarity protection diodes D2 and D3.
When operating from a battery, all the output modules are powered by the +5V line. The jumper links at D0 and D1 must be set to 5V. The voltage of this line is about 0.7V less than the battery voltage due to the forward voltage drop of D3. +PIC supplies the PIC positive connection; it is about 0.5V lower than +5V line (due to the forward voltage drop of the schottky diode D4). D4 and C5 ensure that the PIC power supply remains stable during the switch on of power hungry output devices and prevents the PIC from crashing under such conditions. The total current drain of the output devices should not exceed 1A (due to the limitations of D3). For higher current drain you could replace D3 with a 1N5400 diode.
When operating from the dc power connector, the maximum current that can be drawn from the +5V line is 100mA which is the current limit of the on-board voltage regulator. A total of up to 1A can be drawn from the D0 and D1 connectors by selecting the +V jumper setting. This is due to the maximum current limitation of D2. For higher currents (up to to 3A) D2 could be replaced with a 1N5400 diode.
Seetrax XLD blocks
PIC20 Design (block) symbol
PIC20 Batt and PIC20 PP Circuit details (with PSU omitted)
There are two blocks in the XLD library for picXplorer20. They have the same arrangement for the PIC and programming connections but different power supplies. Select the appropriate block depending on the power supply arrangement you wish to use. PIC20 Batt is for 6V battery powered systems. PIC20 PP is for mains powered systems (via a suitable power plug). In choosing which block to use, you need to think about the following questions:
| ¡ | Does the system need to be portable? |
| ¡ | Is the average power drain low enough to operate from a battery without frequent replacement? |
| ¡ | Do any of the output modules need to operate from more than 6V? |
PIC20 Batt power supply
Details of power supply for PIC20 Batt
To make PCB design a little easier, especially if implementing as a single sided PCB the on/off switch and power indicator (D8 and R4) could be omitted (by editing the block contents)
PIC20 PP power supply
Details of power supply for PIC20 PP
To make PCB design a little easier, especially if implementing as a single sided PCB the on/off switch and power indicator (D5 and R1) could be omitted (by editing the block contents)
