• Dust mask
• Gloves
• Goggles

Ingredients

• 11.24g Gum Arabic Powder
• 24g Distilled Water
• 6g Glycerine
• 1g Raw Honey

Method

Mix water and gum powder. Avoid clumps by stirring vigorously while sprinkling the powder. Add other ingredients and mix until a consistent liquid (as in no sticky stuff at bottom and fluid at top).

Some gum will still be clumpy. Leave until dissolved and then mix again to ensure consistency.

High Temperature paint is pretty easy to get a hold of. Found roughly 3 ranges: 300 °C, 500°C and 1000°C. The 1000°C range needs to be baked in an oven at 200°C to go hard.

The SPI coms worked fine but the values received as cold (internal) temperature and probe temperature looked like they were random. Ordered 2 and they were both duds. Thought it might be a 5v vs 3.3v issue on the data lines so used a resistor divider network on he Scl and Sd lines on the second module just in case I damaged the first. The culprit unit:

Then ordered another 2 from a different supplier. This time the chip kept on replying with a short to ground. After some investigation the probe negative line was shorted to ground by an intentional track to ground on the PCB. Cut that track to break the connection and voila, error gone.

Last challenge was to get a stable reading. Turns out a 10nF ceramic cap across the thermocouple at the connection to the PCB was good enough. The values were alternating from 15 to 32 degrees before the modification. After the change it was a stable 24 degrees.

Lessons learned:

• Test components received from Ebay before giving feedback.
• The optional cap recommended to reduce noise, is not optional.
• Only trust the OEM parts for fancy features like dual voltage support?

Yes its a pain to keep it up to date so I try to update it whenever I buy stuff and as I use/break things I just update a whiteboard in the workshop or jolt down a note on my phone.

Why do I choose the suppliers I buy from? When designing a project one not only has to be creative in solving a problem but finding cost effective materials for the solution sometimes makes/breaks the viability of a solution. If you can’t cost the solution given a certain set of materials, you can’t evaluate the viability and ability of fellow hobbyists to obtain the material. If nobody can get a hold of that special grade Alu or electronic component I used, I am the only person that will build the project. That does seem like a bit of a waste of valuable time and effort to document the plans for other people.

Without further ado, the list:

If anyone has a regular supplier in Brisbane that they use for electronic components, materials and tools, do feel free to add it in the comments. If they see my business I will add them to my list.

Here’s the circuit:

Pretty straight forward, 12V in 3.3V out. Built a couple of these before and they all worked without hassle. Not this one!

Switches on, works for 1-2 seconds and then the voltage drops over the input terminal and the LDO (LM1117) starts heating up. The same happened on a regulator (78L05ACP).

What’s wrong you might ask? After fiddling a bit with the capacitors, I found that they would start heating up when you swap them in and out of the circuit. Turns out I had the polarity wrong. Haven’t used SMD components a lot and on SMD caps the solid line usually indicates the positive terminal, unlike through-hole caps where the line is on the negative terminal’s side.

These were tantalum; guess if it was electrolytic stuff would have gone pop. Interesting symptoms though, a reverse polarity tantalum starts off okay and then avalanches into a dead short. This in turn heats up the capacitor and if it is the capacitor at the output terminal of the LDO, the LDO also starts to heat up pretty quickly. Doesn’t look like there was any permanent damage done. The LDO has built in short-circuit protection and the caps didn’t show any signs of wear and still tested 10uF after multiple rounds of heating up.

All sorted now. Power supply up and running. Now back to the original project: Temperature regulated polystyrene cutter.