I scored some of these analog RGB strips and needed a way to power them, and to be able to control the colours.
Initial prototyping showed that I needed about 20V to be useful, and I could easily switch each colour via a MOSFET driven from a microcontroller. First attempt was with an Arduino, then another with an ESP8266. At this point, I realised that you have to choose the MOSFET gate voltage to suit the logic, so common IRF540 devices won’t work with the 3.3 V available to ESP devices. I selected IRLB8271 instead, and this works.
I have tried a few different circuits, involving different coding.
Cycling through colours
Random colour cycle
Running a web server, using a web page to choose colours
Now to get from the breadboard to a finished circuit …
This year with students back in the classroom it was time to resume the development process. I was able to use a professional development day in Term 2 to finally get to grips with KiCad. I had already looked at a tutorial so using that as a reference I started the process to turn this circuit into a finished PCB that I could use in classes.
Following the steps in the KiCad tutorial I was able to create the circuit, then export this to a board design, choosing the appropriate footprints for components. Next step was to do the layout and connect up the tracks.
KiCad has a very neat 3D viewer which means you can view a finished board before it even gets produced.
Previously I had ordered some PCBs from others’ designs from PCBWay as a test. From KiCad I was able to export my board layers as Gerber files. PCBWay has a quick feature where you just upload the Gerber files and it does all of the configuration. Their prototype rate means that you can get 10 boards made for just USD$5, but unfortunately the shipping costs rather more. Nevertheless, the service is incredibly quick, from submitting the order on Wednesday to receiving it on Monday morning, from China to Australia. The unit cost will come down when I order larger numbers for production.
When the boards arrived, 5 minutes work with the soldering iron and a finished product.
The next step involved transferring this to strip board so they could make a permanent circuit to take home. This part of the process proved troublesome as Veroboard is difficult to work with due to the close spacing of tracks, and the inability of students to follow placement instructions precisely.
In 2020 we started the year, but then COVID-19 intervened and students did not attend school, so did not build physical projects or do soldering.
Picked up a couple of dead hi-fi amps, one of them being this nice Rotel RA-820. Opened it up, gave it a clean and replaced all the electrolytics and back in business. Now sitting in the garage hi-fi cabinet for when I’m working down there.
similar model (RA-820BX) useful photo reference but different values
The other amp is a Cambridge Audio A-300 (like this A-500) but it looks to be in rather a sorry state, with at least one blown output stage. Have to work out whether that one is going to be worth restoring, or may get rebuilt as a chip amp …
This clever piece of tech was behind much of the pop music of the 80s. I picked one up second hand sometime later, and had some fun with it. I got it out of the cupboard last year to fire it up, but sadly it wasn’t working. Nothing. Nada. Not a sausage. I opened it up, did some quick checks and established that the power supply seemed to be problem. Because these things were produced in the hundreds of thousands, there is plenty of information around. I found service manuals that show part layouts and circuit diagrams. A forum suggested that it was likely to be the electrolytic capacitors that would fail in the power supply.
I desoldered the old capacitors, and several of them tested as a short circuit. I ordered the required values online, and had them a week ago, but finally had time today to replace them. Very pleased to find that the synth powers up, and all of the presets are still saved as well. 9 capacitors worth about $10 and it is back in action.
Here’s a really easy demonstration of how you can control outputs on the NodeMCU with a simple web interface. The NodeMCU runs as a simple web server, writing a control panel interface directly as HTML.
The circuit is very simple, just four LEDs with resistors wired to outputs of the NodeMCU.
Here’s the wiring I used, which matches the code.
yellow – D1 = GPIO5
green – D2 = GPIO4
blue – D3 = GPIO0
red – D7 = GPIO13
In Arduino code, GPIO numbers map to Arduino digital outputs, so to turn on yellow LED use digitalWrite(5, HIGH)
Board type in Arduino IDE is ‘Node MCU 1.0 (ESP-12E Module)’
You will need to set up your Arduino IDE to work with the NodeMCU. A good guide can be found at https://www.circuito.io/blog/nodemcu-esp8266/ (go to the last section Programming NodeMCU with Arduino IDE. Note there is a slight typo in the instructions, the board URL should end with ‘.json’ not ‘.jso’).
Upload the code to the NodeMCU.
When it has finished loading, quickly open the Serial Monitor, set the baud rate to 115200.
Wait until the device joins the WiFi network, and note the IP address it obtains.
Enter this address in a web browser, and the interface will load.
Now you can turn on and off the various coloured LEDs by clicking on the respective buttons.
How much do you have to spend on a robot for the classroom? There is a profusion of expensive, shiny toys on the market being promoted for STEM education, but this isn’t the only way to do robotics.
Here’s my prototype bare-bones robot. There’s nothing really new here, it’s just a couple of motors, a motor controller and an Arduino Nano board. It’s just to show how the most basic robot could be built as a starting point for my students to start thinking about their designs. There’s less than $20 worth of parts (if you buy directly from China, and order in bulk).
In this form it doesn’t do much, but the idea is that students will use the basic design as a platform on which to create their own unique projects. They have to think about what to use for a chassis, how to control it (IR, Bluetooth, WiFi, RF?), to put LEDs on it, sensors and so on.