Flashing LED's

I built this...

The idea was to fill the board but I didn't have enough capacitors, so I just did a few stages.

The circuit looks like...

I wanted to draw that up quick, so I used EasyEDA.  It was the first time I used it and was very impressed.  The transistors I built with were BCW66G's although any small signal transistor should work.
For the thing to oscillate requires an odd number of stages. I built 7 stages. Maybe someone will build more :)

Ok, so now I added this..

To switch it on when it goes dark.  The seven stage 'led thing' draws about 6mA when on.  When powered by the dark switch, I couldn't measure current draw (below 1uA) while in a lit room.  The LED used in the switch was a clear red led out the junk.  When light the LED passes enough current to switch Q1 on enough to pull the gate of M1 low.  When dark R1 charges M1 gate up and switches on the upper circuit.

Home automation

Our house has many radiators and seems hard work to heat up properly.  All the radiators bar one have TRV's, but at night we only want three rooms heating up.  The plan is to zone the heating.

I have had a look around and seen many home automation kits that will zone my heating.  They are all expensive and don't quite do what I want.

I got some of these from Maplin, they were only £15 for three...

They come with a remote control and a battery for the remote.

Very nice.  I opened up the sockets, which requires a security bit, to check the quality of the units.  They are fine and no surprises about whats in there.
Inside the remote there is the usual SAW oscillator driven by an encoder chip.  The chip in question is SC5262S.  A simple chip that serializes a number of input pins.  As far as the remote goes, knowing the encoding scheme and transmission frequency are all I need it for so I'll put it in the junk drawer.
I want to control the sockets from my PC so a PIC16F1455 (Microcontroller with USB in a 14 pin package :) coupled to a 433MHz oscillator should do the job...

I built a 'prototype' oscillator on a bit of board using surface mount components...

There are components there! The schematic is 'as built' and it oscillates at about 431MHz.  Thats quite a way off the calculated 635MHz of the schematic, but what can you expect from what looks like a blob of solder.

Theremin

I have been wanting to build a Theremin for ages, so I have started.

There is a YouTube video HERE so you get the idea of what is going on.

To start I need some oscillators.  I have chosen this for an oscillator for no other reason than I like it and have been wanting to design it into something for a while.

Its a 'lambda diode' oscillator, which is basically using the 'lambda diode' in its negative resistance region.  I need two of these, one reference oscillator and the other that will be detuned by your hand.

The output of these oscillators go to a mixer.  To prevent the two oscillators 'pulling' each other, the mixer is this....

With the two oscillators built and connected to the mixer, thats the basic Theremin done.  One oscillator requires a small tuning capacitor across its main tank capacitor to get both oscillators running at the same frequuency.  The other oscillator has an aerial connected to the top end of its L-C tank, this is where your hand waves about.

Next I need to build the volume control bit and something to drive a speaker...

This is the pitch oscillators and mixer with a speaker amplifier.  The volume oscillator and associated bits aren't shown in this schematic.

I'll put up pictures of the prototype shortly and a full nice schematic.

Lightning detector

I wanted to build a lighning detector with a display that would show lightning activity and strength.  I wanted the thing to run from batteries, draw less than 1mA, detect lightning and have some sort of display.  I Googled lightning detectors and found some commercial units and some construction projects.  This page www.techlib.com/electronics/lightning.html is great and gave some good ideas.

But I didn't want to rip off someone elses stuff and the design constraints I had put in place were pretty tight so I started from scratch...

Detecting lightning requires 'listening' for the RF energy produced during a thunder storm.  Any AM radio can detect this, so build an AM radio, connect it to something that will register the loud pops and crackles from the lightning and your done.

Display
I decided the display power requirements were 2V to 5V at no more than 500uA.  I wanted an LED display that would show how often the lightning was occurring.
LED's are realy efficient now and putting 250uA through some white ones I had on my desk gave a satisfactory light output.  The LED's would need multiplexing since I could only light them one at once.  Again going with what was at hand I used a PIC16LF819, which when clocked at 31kHz only draws about 7uA.
   
Radio
I wanted a simple AM radio front end that would use a ferrite bar antenna so it would fit nicely in a box.  I have collected hundreds of circuit ideas that would suffice so I tried out one I had on a scrap of paper...
 

      This worked quite well but then I got obsessed with building an AM radio that tuned the LW and MW bands.  The radio I needed would tune to somewhere below 500kHz, peak detect the received signal and buffer it for sampling by the PIC.  The test circuit is shown below, its a simple reflex receiver followed by an amplifier and peak detector.  It uses a moving coil meter as the display.


The coil is a LW radio coil wound on a 12cm ferrite rod.  The meter is a 1mA FSD moving coil meter.  The detector draws under 500uA from a 5V supply.
      

Wireless thermostat

So we have one of these Salus RT500RF Wireless thermostats..

So far its working ok.  The thermostat is quite long winded to set up.  If you don't want a timezoned background temperature the least you can get away with is programming 10 time zones to the same temperature, aint nobody got time for that.

I think we can do better...
I have cobbled together a PIC16F1455 with an RFM12B and should soon be able to switch the boiler on and off from my PC.

Cobbled together USB Radio...

Not very neat and not a good photo, but it receives and transmits on selectable frequencies around 868MHz.

This continues in my 'home automation' post...