Controls redesign for a food-waste liquefier

A prototype machine that turns food waste into liquid, given controls that are quick to assemble, easy to troubleshoot and simple to service in the field.

Wiringabout 120 hand-wired screw terminals down to a handful of plug-in connectors
Assemblycontrols and harness from about 30 hours to about 3, by my estimate
Prototypeplaced at a local orchard

Loading food waste into the liquefier.

The machine and where it started

Food waste goes into a tub, where augers break it down and the liquid drains out through screens. This was before Atrick Design, while I was the product developer at a Connecticut contract manufacturer. An existing prototype was refurbished and improved. My part was the controls wiring, the circuit board and the operator screen, plus the auger drawings and the shaft seals.

The prototype's control board used screw terminals, with every wire run by hand, about 120 of them going to the board. Changing anything meant unscrewing wires from the board and wiring them back in. Swapping a board meant getting every one of those wires back in the right spot. I could do it, but I would not expect anyone in the field to.

The prototype also ran plastic augers on hexagonal shafts. The new augers are very thick stainless steel, made to my finished drawings by a company that builds augers for industrial processing.

Two white plastic augers inside the machine's tub, on the original prototype — Before: the prototype's plastic augers.

Thick stainless steel augers in the tub, working through a load of fruit and onion waste — After: the stainless augers, made to my drawings, working through a load of food waste.

Controls built to be assembled and serviced

I designed the controls wiring and a new circuit board where the harnesses plug in: about six multi-wire connectors, plus power and USB for the small board computer. A board can be swapped without rewiring the machine.

An indicator LED on every digital input and output, for easy troubleshooting.
Wear parts in sockets, for quick field repairs.
An input for an ultrasonic level sensor, so anyone can see at a glance whether the machine is full or empty.
Timing and sequencing to automatically add the powdered culture that digests the food, built in and ready for the dosing hopper that was the client's next step.

On the controls panel, high voltage sits below and low voltage above. A wiring diagram is laser etched onto the mounting plate itself, so anyone wiring or servicing the machine can see where each wire goes and what it is.

Food also kept getting packed into the shaft seals. I changed them to a stack of PTFE V-ring packing seals, backed by a rubber dual-lip seal.

3D view of the controller circuit board layout, with relays along one edge and grouped connectors — The board layout. Each connector carries a group of wires.

The finished controller board with a small board computer mounted on a steel panel — The finished board on its mounting panel.

Controls panel in the machine during the build, with the controller board above and two motor drives and power components below — The controls panel during the build: low voltage above, high voltage below, with the etched wiring diagram at the bottom right. The cardboard protected the wires from the sheet-metal edges while everything was pulled in; the harnesses were then fastened with snap-in zip ties.

Operator screen showing the tub and augers, with mix, flush, wait, add enzymes and add water status, a waste level bar and door, e-stop, jam and slow drain alerts — The operator screen I designed. Everything in one view.

One screen for everything

I designed the operator screen and its graphics. It shows every normal operating value in one view: what the augers are doing, the waste level, and alerts for an open door, the emergency stop, a jam or a slow drain. Separate user and service menus keep settings out of the way, and built-in input and output tests help with troubleshooting.

The PLC programming and the Linux-side code were done by others, with the code written to my screen design. Others also did the sheet metal.

A prototype at an orchard

This was a prototype. It was placed at a local orchard, which was happy with it for the roughly five months until I left the contract manufacturer and lost touch with the project.

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