Thursday 3 December 2015

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.

Wednesday 2 December 2015

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.