Hacking Cheap Chinese PID Temperature Controllers

[Harvs] hacked a cheap PID controller he found on eBay to improve its performance. The controller originally used a K-type thermocouple but lacked cold junction compensation. As thermocouples only provide a differential measurement between the measurement junction and cold junction, this meant the controller was assuming the cold junction was at room temperature, and would in many cases be significantly inaccurate. The system also used a no-name brand Chinese microcontroller making firmware hacks impractical.

[Harvs] decided that even with cold junction compensation a K-type thermocouple wasn’t ideal for his application anyway, and designed a replacement PCB to interface to the display and power supply. The new PCB is based around a Cypress PsoC (a popular choice for its great analog functionality) with a DS18B20 temperature sensor. At the lower temperature ranges [Harvs] is interested in the DS18B20 is far more accurate and easy to use than the thermocouple.

Though the project hasn’t been updated recently, [Harvs] was planning on adding an ESP8266 for remote monitoring and control. Great work [Harvs]!

Thanks to Peter for the tip.

Overhauling a 3-Zone Reflow Oven

[Ed] owns a 3-zone reflow oven (which he coincidently uses to manufacture reflow oven controllers), but its performance has gotten worse and worse over time. The speed of the conveyer belt became so inconsistent that most boards run through the oven weren’t completely reflowed. [Ed] decided to rip out the guts of the oven and replace it with an Arduino, solving the belt problem and replacing the oven’s user-unfriendly interface

When [Ed] was looking into his belt speed problem, he discovered that the belt motor was controlled by an adjustable linear regulator with no feedback. Although this seems a bit sketchy by itself, the motor also had some mechanical issues and [Ed] ended up replacing it entirely. After realizing that closed-loop speed control would really help make the oven more consistent, [Ed] decided to overhaul all of the electronics in the oven.

[Ed] wanted to make as little custom hardware as possible, so he started out with an Arduino Mega and some MAX31855’s that measure multiple thermocouples in the oven. The Arduino controls the belt speed and runs PID loops which control heating elements in each of the oven’s 3 zones. The Arduino can be programmed with different profiles (stored in EEPROM) which are made up of 3 zone temperatures and a conveyor speed. Don’t have a 3-zone oven of your own to hack? Check out some DIY reflow oven builds we’ve featured before.

Melting Chocolate – FOR SCIENCE!

The Ultimate Fondu Melting Pot

[Patrick Herd] was in Sweden recently and decided to help out a team of high school students in the International Young Physicist Tournament — The challenge? Chocolate Hysteresis.

Chocolate what? When chocolate melts, it doesn’t actually re-solidify at it’s melting point — in fact, it’s quite below that. The challenge here is figuring out a scientific way of measuring the time (and temperature) it takes to return to a solid state. This in itself is kind of tricky considering you have to accurately measure the temperature and be able to empirically tell if its solid or liquid.

The first scientific apparatus they came up with was the Chocolate Rig V1 – a very simple peltier heated and cooled calorimeter. They used an Arduino to control the temperature and a motor shield to power the peltier plate. It kind of worked but they discovered it was difficult to assess the physical state of the chocolate. This is when [Patrick] started doing some research and discovered rotary viscometry.

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