So I’m having thoughts of wiring my house with a bunch of sensors but would like to limit the amount of wires as much as possible. Ofcourse that would best be done with some kind of OneWire circuit. One wire for ground and one wire for data and power.
I’ve experimented in Falstad’s circuit emulator and so far this is what I’ve come up with.
The 470uF capacitor keeps the remote circuit (here its just a 1k resistor) powered while the data line (A) is pulled to ground to send signals. The resistor-transistor at the power source limits the current so it won’t short-circuit. The switch will be replaced with a MCU of some sort to control the sending of data.
I’m thinking of CLR, DATA and CLK going into a 74HC164 serial-to-parallel chip. Pulling the data wire (A) to ground very briefly would latch a 1 (one) as CLK goes back high, pulling it to ground a little bit longer would drain the 4.7uF capacitor enough to register a 0 (zero) when CLK goes high and finally pulling the wire to ground long enough to drain the 10uF capacitor would make CLR go low and reset the HC164 (asynchronous active low).
Timing depends on the values of the capacitors. Ofcourse at point (B) the voltage to power the MCU would be only 3V, but an atmega or attiny will run on that. It’s even possible to have several sensor circuits on the same two wires.
Now I just have to go from drawingboard to physical circuit and make it work…
“Psst. Hey dude. Over here…”
A chinese man in the shadows beckons me to come over. When I do, he opens his coat to show me the lining covered with little bags full of INTEGRATED LOGIC CIRCUITS.
The mans name is Ali. Ali Express. And while he claims his goods are the best, straight from the factory, it can sometimes be something entirely different. But, most of the time it gets the job done.
Ali has been my supplier for a while now. Sometimes his wares are scruffy but it’s usually not an outright disappointment.
Today he dropped another small bag at our secret drop box. It was filled with… well, see for yourself. Plastic cases or foam was not included ofcourse. Alis wares usually comes wrapped in horrible kitchen plastic foil. Cringeworthy stuff having near static sensitive devices. But hey, it’s cheap.
All of this for 11 dollars, 13 cents. Shipping included. But Ali made a mistake this time, I only ordered and paid for 2x ATTINY85s, but I received 5x.
My uncle also dropped by today and left a few (three) PIC16C84-04/P chips as well. So now I’m all set up with MCUs for a while. No more excuses, it’s time to get around to doing something useful…
After hooking up eight LED matrices in series, I could see that the LedControl library wasnt up to the task. After digging through the source code I realized what a peice of junk it was.
I had to do better myself. And did. I even ended up writing my new routine in assembler. Better optimized than even the code gcc managed to produce.
Source code in the form of an Atmel Studio project,
is available here: http://joonicks.eu/arduino/LedControl.zip
Finally got around to making a demonstration video of my current limiting and short circuit protection circuit.
Using a LED as a dummy load might not have been the best idea but at least it visualizes the concept in a simple way.
The circuit is intended as an extra protection layer between a power supply and the circuit that uses it. Instead of blowing fuses or magic smoke in case of overcurrent or short circuit, this concept circuit could be tuned to protect the power supply quite well and cheaply.
Though in case of bigger normal loads, the transistor cant be a flimsy BC547. With any luck it might manage a few hundred mA but at 500 mA it’d probably burn up pretty quick.
“Bigger” package arrived today from China. A whole bunch of good stuff. But a lot of it also needs header soldering before it can be put to use. The two ESP-12F modules will be especially tricky to solder any kind of headers on to, seeing as the connection points are not spaced the standard breadbord friendly distance.
View the unboxing video on Youtube here: https://youtu.be/q4k5O6LL3a8
Its also my first unboxing video, so dont expect too much.
A small package arrived from far far awar with some new playthings for me.
- A small 128×32 pixel OLED display, I2C interface.
- 433MHz transmitter and receiver (two separate modules)
- Four 7-segment 4-digit LED thingamajingys
- Header pins…
Got the OLED working pretty quick.
Inspired by Kevin Darrahs video on Low Power Arduino! Deep Sleep Tutorial, I set out to see if I could apply some power saving to the basic blink program.
After the usual trial and error, I did get results. Normal current usage of lit/unlit Arduino nano running blink is 14/12mA. Replacing delay() with my own function going to sleep in power-down mode reduced the current to 6.6/4.6mA.
The power LED is always lit, consuming 2mA. Kevin was running his tests on a breadboard Atmega328P, obviously the Nano has a bunch more circuitry so thats where a bunch of current goes to.
And also, both the Arduino Nano and Arduino UNO will happily run off a 4 volt battery. Just connect + to the 5V rail (not VIN) and – to GND. I was using a battery from a mobile phone (nominal 3.7V but fully charged to 4V).
Source can be found here: PowerBlink.ino