Arduino Autoclave Stopwatch With Display and Buzzer

My client has some older autoclaves which are completely manual in function. Client's product is required to cure in the autoclave for 60-90 minutes depending on the size of the project. The client has historically used a timer (counting down to zero) but issues arose if the timer wasn't initially set properly, the timer ended and it couldn't be known for how long ago it ended, or if a shift change occurred and the new employees wouldn't know that the autoclave was running.

This setup displays the autoclave pressure (displayed as P) at any given time. Once the pressure gets to 40 psi, the stopwatch starts counting up in minutes (displayed as T) and doesn't stop counting up until the pressure drops below 20 psi. From 0-60 minutes the display is green, from 61-90 it is yellow, and beyond 90 minutes it is red so that anyone in the shop can immediately tell the relative time range. At 96 minutes a buzzer begins to go off until the stopwatch is reset by reducing pressure.

Display $24.95 https://www.adafruit.com/product/420

Matrix shield $5.95 https://www.adafruit.com/product/2601

Pressure Sensor $18.69 https://www.amazon.com/Pressure-Transducer-Sender...

Uno R3 $13.98 https://www.amazon.com/ELEGOO-Board-ATmega328P-AT...

Power supply $10.99 https://www.amazon.com/SHNITPWR-Converter-Transfo...

Project Box $9.99 https://www.xump.com/science/Electronics-Project-...

3 Lead Wire $12.38 https://www.homedepot.com/p/Southwire-50-ft-18-3-...

Buzzers $8.99 https://www.amazon.com/Cylewet-Electronic-Sounder...

Display screws $7.99 https://www.amazon.com/uxcell-M3x8mm-Thread-Butto...

Display Washers $4.99 https://www.amazon.com/Sutemribor-M3x6mmx0-5mm-St...

Terminal strip block $12.89 https://www.amazon.com/Positions-Terminal-Pre-Ins...

I cut a notch in the main portion of the project box for the outside wires to run. On the lid of the project box was where I mounted the display and on the backside of the lid (inside of the box) is where I mounted the Arduino using double-sided tape as well as one of the display mounting screws run through the factory hole of the Arduino.

I drilled the display mounting holes and either drilled or used a hot knife to make the holes for the display's power and signal cables.

By mounting all of the electronics to the lid, it makes servicing the unit in the future very easy.

Solder the pins and connectors that come with the Matrix Shield into the Matrix Shield.

Connect the Matrix Shield to the Arduino Uno.

Plug the LED display power cable into the LED display and connect the other end to the Matrix Shield using the screw terminals.

Connect the GPIO ribbon cable to both the LED display and the Matrix Shield.

Solder an approximately 8 inch section of 3 lead cable to power (Red), ground (White), and port A4 (Green) of the Matrix Shield.

Solder an approximately 8 inch section of single lead cable to A5 of the Matrix Shield.

Pictured is how the arduino should be mounted to the lid using the mounting screw and the double sided tape. The GPIO ribbon cable that comes with the display can be too short if connected backwards. If it's too short then reverse the GPIO connectors.

Secure the box lid to the box with the power and GPIO ribbon tucked neatly inside and with the 4 leads of cable running to the outside of the box through the previously made cutout.

Power the Arduino using the 5V power supply which should be at least 3 amps. Program the Arduino using the attached code. Programming and powering the Arduino should be easy because of the notch made in the project box. Pressure will fluctuate on the display until the sensor is connected or a resistor is set across the power and signal leads. Be sure to download the display libraries correctly.

Mount the terminal block to the bottom middle of the housing and the buzzer to the bottom right of the housing (opposite the cutout) with the buzzer leads directed towards the terminal block. Connect the four leads from the Arduino to each of the terminal block's contacts.

Buzzer Connection:

On the other side of the terminal block, connect the buzzer hot to the single A5 wire coming from the Arduino and connect the buzzer ground to the white wire coming from the Arduino.

Pressure Sensor Connection:

The pressure sensor has three leads: power (red), ground (black), and signal (green). Connect these three wires to the terminal block with the green sensor signal wire going to the green Arduino wire and the black sensor wire going to the white Arduino ground.

Notes on daisy chaining:

Multiple displays can use a single common 3A power supply. Simply connect the power connection of one terminal block to the power connection of another terminal block and the same with the grounds. I powered three displays with one 3 Amp power supply.