Garbage Truck PCB

• Controls hydraulic Rams (thru FET driven solenoids) to compress load on a garbage truck

• Simple robust construction using 8 bit microprocessor and DS PTH board

• Robust protection against power supply and I/O transients

Circuit Diagram

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Bill of materials

Parts list and notes

PCB design

Using a simple mircroprocessor did mean that a few more parts were required for completion - for instance in this type of circuit a watchdog reset is essential, and this is implemented in discrete circuitry using two parts of a 4093 as a gated oscillator and power supply level sensor. However this older microprocessor is a very standard type, easily debugged and replaceable should software update ever be required.

A large filter capacitor is used on the +12V supply circuit, together with a transient clamp and reverse polarity protection. Back-emf diodes are placed on the FET outputs running the solenoides.

As with many of our projects there was a diagnostic serial port on the unit to allow us to test and debug the sensor inputs to the unit, to test operation over the full range of conditions. Together with a few spare I/O lines, this comes out on CN3 Extension connnector, which is unused in the final application,

Final board

Rotary connector diagram

Documentation package