Tuesday, March 3, 2009

My first SMT build

I saw a PIC Logic Tester kit being offered by JayCar which uses SMDs. I built a TTL/CMOS probe in my previous life as a hardware designer in the 70s but hadn't updated to the new lower power technologies. I need a logic probe so this was a good start.

Kit arrived this afternoon and I nearly died when I saw how small the components really are. But under the magnifying lamp I could read their values or markings and the PCB looked a lot clearer. So I fired up my new soldering iron and commenced work.

Six hours later it's finished. Lots of problems encountered and overcome. The worst was when I squeezed too hard on the tweezers and a capacitor shot out and I have no idea where in the room it landed. I spent 15 minutes looking but couldn't find it, so decided to proceed without it, hoping it wasn't too critical. But then I found it under the board itself. 0603 components are the worst for hand assembly.

I also discovered I probably had the iron too cold initially. I started with 350C but moved it to 375C and joins seemed a lot quicker and 'wetter'.

Now I've realised I don't have a circuit to test it on so my next project will be to use the FreeScale sample chip I got a while ago to build a simple counter or whatever and I can check my new logic probe on that.

I was delighted to run the 'blinktest' demo program on my S40C18 and display a 291Hz square wave from one of the pins on my new oscilloscope.

Relearning and retraining

I walked away from a high-paying contract into the middle of an economic downturn/recession/depression/meltdown/end_of_the_world_as_we_know_it. I keep asking myself is it really better to starve for one's beliefs? I just couldn't take the client's money anymore when I knew I wasn't doing anything useful for the client, I hated what I was doing and I realised that I was even losing skills in areas I wanted to work in (e.g. Perl and web development).

So here we are three months later and not a nibble for any of the jobs I've applied for and most of those jobs don't look all that interesting.

So in the meantime I've started self-educating in a completely different area of IT from how I've earned my living for the past 20 years: embedded microcontrollers.

I've been quite overwhelmed by the amount of learning I will have to undertake to program the SEAForth chip I bought. Obviously there's Forth and Intellasys's version of it,VentureForth. Then there's the SEAForth chip itself which is a Forth machine (in fact there's 40 cores, i.e. 40 Forth machines.) Three of the cores have an ADC and DAC each and so I'll need to know more about digital filtering.

The S40C18 doesn't come with much of a library (so far) and there is no USB, HTTP, Bluetooth or WiFi stack in the current version. So presumably I will have to implement my own if I want to use the chip for any sort of comms app.

My initial idea of implementing a wireless microphone adapter has gone through a lot of ups and downs as various chips and articles in magazines look almost to have done what I want but (so far) there is always one or more of my requirements missing.

My initial optimism that the S40C18 would be able to handle the whole task in a single chip has been dashed when I learned that although the individual cores run at approx. 900MHz, the DAC isn't fast enough to run at these speeds. So my design needs some sort of additional chip if I want to use Bluetooth or WiFi. But USB-WiFi adapters are less than $10 so that's not a big issue.

It occurred to me that all the ideas I've had so far for the S40C18 are all variations on the same set of functions. In addition to a wireless microphone, I've thought of implementing a software-defined radio, a guitar-effects stompbox and a digital oscilloscope/logic analyser. All of these use basically the same parts: a signal digitiser (ADC), some filters and a USB or HTTP or WiFI output.

Another area of study was prompted by holding the S40C18 eval board in my hand. I could barely see most of the components let alone work out what they are. Surface-mount devices are obviously where it's at these days. So this prompted me to embark on a hasty update to my hardware assembly skills. I emailed a friend who I know has done some SMT work asking for help for what equipment I need to build SMT circuits and he replied with a multi-page article which he ought to publish, it is so useful.

So I bought a DMM/Oscilloscope, a new soldering station with really fine bits for SMT work, a magnifying lamp, some breadboards, solder, hookup wire and some other bits I've forgotten already.

And so the great hardware adventure begins...