Wednesday, December 30, 2009

One 8 step sequencer running on the bench

I spent a bit too much time googling for synth music and sequencers over the last few days. I had a lot of fun just reading about folks projects and how they built up various kits or designed from scratch different arrangements. I have not really spent much time working with 4000 series or 7400 series ICs in the last ten years. Well not since first year Uni to be honest. That was a long time ago and my memory for truth tables is long forgotten.

So, I almost cheated but finding the friendliest schematic I could find and trying to build that up. You know how it goes, adapting part of this circuit as a stage one of your project. Well I had a few problems. My 4017 wasn't behaving at all! I spent several hours on the bench trying to figure out why I couldn't get the thing to behave. The first problem was that I missed a ground connection on pin 12, eventually running a bypass cap to the reset pin before it settled down and started to do the right thing. But the first LED wasn't behaving itself at all ...

Some further testing revealed that the LED in the first position was a flashing LED! So its now in its own draw, in the component cabinet. The 555 was a whole lot easier to work with and was pretty much doing what it was supposed to from assembly. The potentiometer has a dead spot right at the fast end of oscillator, so may need to swap the wires on the pads, or get a new 1megaohm 'pot'.

I will say that after having the 'friendly' schematic, I did change most the resistor values, add a few extra capacitors and lay it up differently on the plug-in breadboard. Its not a new circuit, but I learned a lot, mainly how to trouble shoot this little thing.

So what have I achieved here? More motivation to tinker in the shed/shack on the plug-in breadboard and play around with the circuit. Getting things working build up the motivation to do more. I have a tall ladder before me. I'm aiming to make the rungs nice a close together. Easier to climb that way ;)

Anyhow, happy homebrewing to all!



Monday, December 28, 2009

one dual rail 12V PSU on the bench and working

Spent a couple of hours researching and then building, testing/destroying, then researching and re-engineering a dual rail power supply for +12 volts & -12 volts.

Not sure what kicked it off, but I am kind of over my 10 meter QRSS receiver not working. I was looking at a ham radio blog, found a video of NE555 and 4017 based synth sequencer. Down the rabbit hole I went reading dozens of web pages, until finally finding the coolest sequencer I've ever seen!

On the Natural Rythm Music site I found a 16 step rotary analog sequencer. It is a visually amazing device, certainly feels more intuitive than you regular 4 blocks of 4 linear sequencer. The builder has a great presentation style and can put together some cool tracks.

This discovery then in turn inspired more and more reading until I found some basic building blocks. Everything seemed to need a dual rail power supply, so I though I should start there. Some web searching, followed by checking a couple of different editions of the ARRL handbook led to a simple dual rail regulated supply. I carefully noted down the schematic, made a parts list and marched off to the shed/shack to build.

Stepping back a ways, I purchased for two dollars, a two amp twelve volt power supply at the radio club meeting. I was a bit disappointed that it didn't work, but put it aside for a rainy days hacking I suppose its the risk you take when you buy gear from a deceased estate, no real history on the item. So yesterday was that day, except it was 32c, no rain and no wind. Makes the shack a little warm.

I amassed all the parts, dissected the old power supply, noted the two 10,000uf 24 volt electrolytic capacitors and carefully discharged then with a long screw driver... the spark was impressive for a power supply that had been unplugged and idle for six months. Note to self, be careful around these caps!

Spent a while working out the arrangement on tag strip, then manhattan style, but didn't find a nice way to mount everthing in the space available. Got a coffee then came back with the lost thoughts of some veroboard of yore...

Found the vero board and worked out a layout on the board from the schematic. Assembled it, checked it twice. Carefully hooked everything up and turned on the power. Everything looked Ok until the LM7812 regulator launched a small part of itself into orbit!

Ok, this wasn't part of the plan! Turned everything off, disconnected everything and started the autopsy. Everything was correct according the schematic. So I checked the schematic against the original. Sure enough the pin out of the LM7812 was wrong and had exchanged the ground and incoming unregulated power line, pins 1 and 2. No wonder it went FIZZ POP!

I downloaded the data sheets, just to be sure. Who would have thought that the LM7812 and the LM7912 would have different pin outs? I mean really?!?!?

Anyhow, I spent about an hour looking for a replacement regulator. Almost despondent that I'd never found one, I happened to find a little plastic draw that had been missing out of the component cabinet. Interestingly I must have put it aside when I first looked at the power supply and thought about reworking it as a regulated unit for 12 volts for my 2 meter radio.

Anyhow, it all went together more easily the second time and it passed the smoke test the second time, keeping the smoke on the inside! Along with providing 11.99 volts and -12.01 volts. The simple test load this time was a pair of 12 volt 20 milli amp four inch fans from a peecee power supply.

So, now to find all the parts for an audio VCO for tone generation, an LFO for effects, mixer for multiple channels, various high and low pass filters and an amplifier... The aim is that all of these will be building blocks for test equipment for RF down the track. Cunning plan huh?

Monday, December 07, 2009

MTB on the road

I spent some time over the weekend working on the mountain bike I picked up. The complete bike is less than half the weight of my old MTB! Its all aluminium, with the inch wide double walled with eyelets. Currently setup as a single speed, about 70 gear inches. Seems a good balance for pootling around the small hills here. Will fit road tyres at some point in time. Looking at fitting my rack this coming weekend. Then lay up all the gear for a short tour.

VK band plan

Was doing a bit of reading to confirm the frequency range for 15 meters to think through the IF article in this months AR magazine. So 15 meters covers; 21.000 - 21.450 MHz. I have a hand full of 4MHz and 25MHz crystals.

While I was reading through the band plan, I found something new, and entry for 2200 meters. But what grabbed my attention even more was that there was a mention of QRSS;

137.6 - 137.8 kHz Slow CW modes, e.g. QRSS