Little mailbag, January 23rd


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.


Power saving Arduino

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

Raspberry Pi 3 + Slackware

Yesterday I realized I havent even tested the Raspberry Pi 3 that I got from China on the 29th of December, so this evening I spent setting it up.

Since I am an old slackware guy I have been looking at Slackware ARM. I grabbed my biggest MicroSD, a 64GB class 10 card I havent used for anything until now.

Setting up the card for boot was easy. Just dd the downloaded image to the card, dont need to bother about formatting or partitioning because the image contains the partition table already set up.

The installing all the packages took quite some time, but it all went smoothly. Configuring the network took several hours of trial and error though but got it working fine eventually.

In the future I want all my Raspberry/Arduino/ESP8266 devices on a local network even though I have a great ISP and probably could give all the devices a real internet address. But security-wise that wouldnt be the greatest idea ever…

But for now, I just plug in power and my little Raspberry shows up on a local IP listening intently for my ssh input.

I love Slackware. None of that sudo madness that Debian/Raspbian thinks is a security improvement…

Current limiting circuit v11

More experimenting. Only 1 day left of the Multisim trial so I better make good use of it. So… It turns out a couple of those resistors arent necessary, simplifying the circuit. It still works perfectly fine. Short out R5 and the load goes to 450mA, never more.

If the physical circuit works just as fine as in the simultor, this could be quite a nice, cheap circuit to protect me when Im experimenting and hooking up jumper wires all in a mess on a breadboard. Ya never know when the next short circuit will happen.


Wind sensor

From a post on /r/Arduino I had some ideas about how to make a simple wind sensor.


Tested one of the Hall sensors I have with a neodymium magnet I took out of an old CD-ROM. The particular Hall sensor in the breakout board is a 49E501BG. At first I tried another Hall sensor but the output from that one was almost digital, useless.

When I tested it I attached the magnet to the tip of a screwdriver and moved it around in all kinds of ways around the sensor. It gave nice clear readings from 300 with the magnet at its closest to 600 with no magnet or even 800 if the reverse side of the magnet was close.

Pingpong ball would give the wind more to drag on. A dampener (more rubber bands) would be good so that the magnet doesnt move too far away even in a full storm.

Oscilloscope day

Arrival today from Amazon, a cheap (£46) USB oscilloscope. This one is either fake chinese or something, or I was lucky. All the other scopes, same model, were about £60. I havent opened the package yet, so we will see…


This is the lowest end budget version, 2 channels, 20Msps. Have to start somewhere…

Circuit optimizing day

Spent the day trying to optimize my current limiter circuit by testing different kinds of transistors in Multisim.

The one I found that seems to perform the best (according to some metrics) is BD137G which in the simulator has a voltage drop of only 0.03V. Compared to the original BD243CG which has a voltage drop of 0.09V

Here is the schematic: