c. K8055 upgrade from PIC16C745 to PIC18F24J50 or PIC18F26J50

PIC18F24J50 is generally more powerful than PIC16C745. Though it is still an 8-bit processor, it has much bigger RAM and EEPROM. It is pin compatible with older PIC16C745, except for the Vdd (power supply pin) and voltage levels of outputs and inputs. PIC18F24J50 operates on 3.3 V and needs a voltage regulator (ex. LM317T), while PIC16C745 operates on 5 V.

To replace PIC16C745 with PIC18F24J50 on K8055 board you have to add an extension board that has protruding pins that connect onto the socket of PIC16C745. The extension board must also have a socket for PIC18F24J50, +3.3 V voltage regulator based on LM317T and a 4 MHz, 8, MHz, 12 MHz or 16 MHz crystal to be able to communicate via USB at high speed (12 Mb/s). You also need to add a few resistor voltage dividers to adapt input ranged ranges {0 .. +5 V} to {0 .. +3.3 V} and two transistors to adapt output range for PWM (pulse width modulated) signals and D/A from {0 ... +3.3 V} to { +5 V ... 0 V}. You shoult take into account that PWM signals are now reversed, so you have to adapt your programs accordingly (D/AOUT = 1023 - value). Alternatively you can use an adapter version of HEX file (for 4, 12 or 16 MHz crystal resonator). Only a few PIC18F24J50 are + 5 V tolerant (look at shaded pins). We could only use this feature on RC6 and RC7.

The best thing about this adapter is that you do not have to modify K8055 board, so you can place the old PIC16C745 back and vice versa in under a minute.

ALSO READ: Velleman K8055 (K8055-1) USB experiment board easy upgrade

Here is the K8055 to PIC18F24J50 adapter circuit (all connections to the PIC16C745 socket on K8055 board are colored red):

Click on the photo to enlarge