Browsing Posts tagged development

Is that it?

Yesterday afternoon and evening, for me, went with a strange sense of anticlimax.

Nearly everything went according to plan!

Amazing and somewhat off-putting.  This is not how things normally go for a ‘Big Switch On’ on a Wardian project.

Things just worked.  Nothing blew up, there were no tell-tale plumes of blue smoke; there were no bad smells of burning silicon; there were no muffled ‘crumps‘ as something big and expensive died.

So, as the title today suggests, I’m sat here, with a slightly dazed feeling.

How could it all have gone so well?!

Yesterday, I got back from that meeting much later than planned -I’d been kept waiting for over an hour, and there were still a couple of soldering jobs to finish -I had to re-solder the 9-pin serial connector, the power switch and the programming switch so that it would all fit in the box.

Diane texted me saying she’d be round imminently, leaving me barely half an hour to finish it all off.

This was how a project ought to go!

But by the time she’d arrived, miraculously, I’d just about done.  While she made herself a cup of tea, I finished it off, screwed the lid down and switched it on.

Flashing lights, and briefly getting on the bike and pedaling to confirm the PWM was working, yes, it was.

Strange!

Diane took the box, the bike holder and the lights over to The Plots in her car while I cycled over.  This was fun, as the back tire is a ‘slick’ (…to reduce noise when pedaling…), and luckily the roads were quite dry.  Had there been any rain in the air, then I’d have been kissing the backside of a bus as the back tried to catch up with the front when I touched the rear brakes.

Claps and cheers as I arrived (…Thanks, Diane!..), and there were quite a few ‘Junior Plotters’ about.  I’d come down on my bike, was there any chance that the we were having a demonstration of the power project?  Yes, there was.

Initial shouts and cries of disbelief were quickly quelled as I explained that Diane had all the bits in her car.

So myself, Sara, John and Gary put up the three gazebos in an ‘L’ shape, then tie-wrapped the legs together where they met.  Junior Plotters were bouncing around, obviously keen for me to set up the bike, so I eventually gave in and set it up.

Then I had an idea.  The recent light frosts have meant that the nasturtiums on the mound have now mostly died back, but they’ve left their seeds.  You may recall that I pickled a jar’s-worth a few weeks ago, and I was keen to get some more for another pickling session.

So, I told the Plot Kids that I’d only let the taller ones have a go on the bike if they picked me enough nasturtium seeds.  Well, they set off as if possessed, eager to bring me as many of them as possible.  Kyle in particular was very anxious to ‘have a go’.

Is this enough?

Is this enough?

Here he is with the bowl.

After a cursory scout round myself; “You missed this one!  And this!”, I finally, ‘reluctantly’ gave in, and we all went over to the bike.

I switched it on, and yes, as Kyle had requested, they could see the blue LEDs!

I got on, started pedaling, and more lights came on -to show that the PWM was working and that charge was being put back in the battery.

The ‘Grown-Ups’ heard all the commotion and came over, and quite soon, quite a crowd had gathered.

Kyle cycling to keep the lights on.

Kyle cycling to keep the lights on.

We were also celebrating Chloe’s birthday, and various cakes and pastries had been brought to share, so we set them up under one of the gazebos, and here you can see the interest is pretty evenly split between the food on the table and the bike.

In the meantime, nearly everybody ‘had a go’, and here’s Gary doing his ten minutes-worth.

Go for it Gary!

Go for it Gary!

John and I had positioned the lights such that three of them were on the pillar where all three gazebos me in the elbow on the ‘L’ shape with the fourth light shining directly down on the bike itself.  Well, it was centre stage!

Also to note was that there were a couple of comments about the height of the saddle, and Diane in particular found it quite painful to be so low because she has problems with her left hip.  So, before the next ‘outing’, a quick-release adjuster for the height adjuster will be bought.

Another comment was the fact that the bike was positioned so it was ‘pointing uphill’ on the driveway.  This was to counteract the fact that the back wheel is slightly raised by the frame in which it sits, so it ended up being fairly level to ride, rather than feeling like you’re going downhill all the time.

All too soon it was going dark.

Now, on a ‘normal’ Plot Day -as much as one ever can be normal, we always treat the dusk with a ‘groan’ for it means that very soon we have to stop work, but yesterday, we couldn’t wait!

People had started to drift off, but there were just enough of us left to put down the gazebos and stow the equipment away ready for its first ‘official’ outing on Saturday for Halloween.

Control box and cables, lit as it goes dark.

Control box and cables, lit as it goes dark.

Here, you can see a final shot before we packed it all up with the plain black control box, surrounded by the lighting cables, bathed by the light of some of the spotlights.

A suggestion was made that for a future version.  I should make the top out of clear perspex so interested people could look inside.

Of course, people are ‘spoiled’ by ‘Star Trek’  and other sci-fi where there are lights behind all the panels, so if I do make a clear lid, I’ll have to make sure there are plenty of flashing tell-tales.

Of course, people will then ask what each LED represents, so I’ll have to get creative with the various functions inside.  Words like ‘plasma flow injectors’ and ‘wave-guides’ will have to be thought up.  ‘Manifold’ will have to come into is somewhere.

Oh, and there’ll be blue LEDs.

I promise.

Momentous. 22/09/10

Ladies and Gentlemen, tonight something extraordinary happened.

At precisely 8.15pm BST, I sat on the bike, said a little prayer to whichever Gods may have been listening, and started pedalling.

Quite slowly at first, all the time looking for the tell-tale plumes of blue smoke and all the while sniffing the air for that unmistakeable smell of frying silicon.

Nothing.

So I pedalled a little faster…

…And the first green LED lit.  “…Huston, we have a green light on the board.  Ignition set for ‘Go!’…”

My heart was pounding, my stomach somewhere up near my throat.  Still no smoke or burning smell.

I pedalled a little faster still…

…And the other green LED to tell me that charge was being transferred first flickered, then lit properly. “…We have main lift off.  All engines running at 110%…”

I looked over at my multimeter, wired in series with the battery and set to read current.

It flickered, numbers rapidly changing.

So, I pedalled faster still, and kept that speed, and sure enough, both LED’s were still lit, and the meter had settled down to read a steady 0.5 A.  “Huston, we have achieved escape velocity…”

Okay, not earth-shattering numbers here, but its a start!

I had purposefully set the PWM width (…that’s how much I’m putting into the battery…) to be very, very slim, so this was entirely expected.

SO tomorrow, I’m going to pop down to Maplin’s first thing to get a ‘7805’ 5 volt regulator and a few de-coupling capacitors.  When properly wired up, this will mean that the unit is entirely free-standing.  No mains required.  The 7805 will power the little PIC processor and associated circuitry, and the power for that will come from the battery -it certainly won’t hurt any as it only takes a few milliamps.

This will mean that if all goes according to plan (…HA!..), I can take the bike, the circuit board and some lights down to LEAF on Saturday!  Volunteers will be able to ‘have a go’ at charging the battery, and we’ll be able to have lights to see by.

Synchronicity:

Just the other day, I bought a really ancient but otherwise fully working laptop in really gorgeous condition from ‘Taplin Computers’.  This will be used to show photos that we’ve taken while we’re down on The Plots.  The ‘synchronous’ part is that unlike many newer laptops, this one has a nine-pin serial port on it.   With a little initial ‘setting up’, this will connect straight into my little PIC programming board.  This means I’ll be able to make code changes on the site without having to come all the way back here to my main computer.

10.22pm News:

Just checked Maplin’s online, and they’re completely out of stock of ‘7805’ voltage regulators.

However, a good rummage through my parts inventory, and I’ve got a brand new one!

So, my mistress Lady Sleep will probably be a long time coming tonight.  I’d better get to work now then…

Oh, so nearly there.

The sensing resistor block.

The sensing resistor block.

A pretty momentous week, all told.

To the right here, you can see the resistor ‘block’ of ten 0.1 Ohm resistors prior to soldering which when wired in parallel make an astonishing 0.01 Ohms.  This is before they are soldered.

This low resistance is needed to be able to sense the current flowing into the batteries.  I had been using two 1 Ohm resistors in parallel which gave 0.5 Ohms, but found that when I wound up the power supply, the voltage across them -and hence the amplified voltage coming out of the new current sensing i.c. was a little on the high side -even though the current is meant to be limited to 2 Amps or under.

The bike generator will give out over a factor of ten of this, hence the lower value resistors.

The board in the middle of construction.

The board in the middle of construction.

Here you can see the board ‘as I’m building it’ last night.

On the right, you can see the PIC programming board I built so many months ago.  Towards the top of the photo, you can see the ‘new’ board with the little PIC and LEDs on it.  In the middle at the back, you can see the new 0.01 Ohm resistor block I built up last night.  This has been safely mounted using the engineers favourite -Superglue!

Between the two boards and below the new resistor block, you can see two FET’s that switch the power with signals from my new board.

Luckily, unlike normal bi-polar transistors, FETs don’t go into ‘thermal runaway’.  When this happens, a transistor gets hot, so its resistance goes down, therefore heating it up even further and the runaway happens.  The result? A little plume of blue, acrid-smelling smoke, accompanied by the immortal line, “Whoops.  That’s taken the chill off it…”

FETs are much more graceful when it comes to these vexing problems.  When a FET gets hot, its resistance increases, thereby limiting the current, thereby cooling it down.

SO, I’m using two here in parallel in all confidence that neither will blow, and it means I’ve effectively doubled the current-handling of the switching circuit.

Finished!

Finished!

Here we have the finished board.

You can see I’ve mounted the two switching FETs, and if you look really closely, you’ll see they are connected.

Beneath these two FETs is another heatsink with another device on it I haven’t previously mentioned.  This is the final ‘blocking diode’.  This prevents current going backwards into the circuit.  Without it, the cyclist would get a free ride as the pedals would turn themselves.  Not something we are keen to promote!

Anyway, thats it for now.  Wednesday afternoon is a LEAF session and as the weather’s so nice…

Okay, okay…  I can hear what you’re thinking! “When’s he going to get on the bike…???

I’m be leaving early this afternoon, and I’ll come straight back, and yes.  …I’ll get on the bike!

Don’t nag!

Power Update.

For those who just can’t wait!

Quite a lot of running about today (…like a new landline installed here at ‘Wardian Central’ and another visit down to The Quacks…), but inbetween times, I’ve had chance to do quite bit on the power control circuit.

The board is sprouting components.

The board is sprouting components.

If you click a couple of times on the photo to the right here, you’ll notice that the board has ‘grown’ some new bits.

I’ve put another 1 Ohm resistor in parallel with the one stood upright.  This is to effectively double the current measurement range.

I’ve also added a 100 Ohm 3 Watt ‘dummy load’ of the white resistor laid down on its side on the right beneath the red and green LED’s on the right hand side.

Today, I’ve been taking meaurements from the new chip I put in -the current monitor- and checking them against the formula given in the datasheets.

It turns out I’ve blown one of these chips, but thats not a problem.  I have one spare and four more on order and they should arrive by the end of the week.

So, now I’ve got the remaining working chip in place with revised and added-to code in the PIC, everything appears to be checking out okay.

The PWM (Pulse Width Modulation) part of the PIC is working pretty well -there’s just a couple of bytes to change, and its switching between PWM ranges as expected.

When you first turn the circuit on with the power supply giving out zero volts, and as you’d expect, nothing comes out of the circuit and the tell-tales are not lit.

As you turn up the voltage, you reach a point where the green one lights and the PWM kicks into action.  As you increase the voltage, the green tell-tale goes out and the red turns on, and at the moment, the PWM waveform reduces, but this is simply a ‘stupid’ in the coding that I haven’t yet been bothered to put right.  No worries!

Anyway, Dear Reader, I’ll leave it there and carry on.

p.s. And the new ‘Toys’ are brilliant!


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