Geronimo!!

Well the Parachute has turned up.. It is made out of a lovely 'thin mill' fabric and only weighs in at 11 gms so result. We went for the 24" as we worked out it should give us a decent rate of 5.61 meters/sec and should be a safe landing rate...but looking at it....we need to do some testing but "I think we need a bigger boat"

Flashing lights

Phil noticed that our LED was not flashing on receipt of data, but rather flashing on the absence of data. Whilst not exactly required, I decided to include an inverter circuit so that the LED would operate as expected. It sounds impressive, but it's a very simple circuit requiring no more than a couple of resistors and an NPN transistor.

This has been tested and it works fine. Whether it's a good idea to build it onto the production board, I'm not so sure. It adds complexity to a circuit that although should be simple, we've had enough problems on the stripboard to prove otherwise.

This will be the last you will hear from me until the 21st September as I'm off on a break. Hopefully Phil will be here to keep you upto date on the latest whilst I'm away. See you in a few weeks!

Back to basics...

...back to the breadboard. I've rebuilt the receiver on the breadboard and all appears well. Why the circuit never worked (properly) on stripboard is a mystery, but it confirms that we weren't doing anything very wrong - and that the components are working.

One of the things Andy wanted to work was a flashing LED to show that the device was in fact receiving data. This was lacking from the original design and so never made it to the stripboard version. Now that we are back on the breadboard I've had a chance to try a couple of things, the result of which is... a flashing LED when data is received.

With both circuits fully working, we need to make an effort to get these into their 'production' state. In the meantime we are waiting for our camera to be returned as it died shortly after arriving and before we could even load the new firmware - let alone test it.

Troubleshooting: Day 3

Another frustrating day. Everything that can be tested has been tested, yet we're still no closer to finding out why we get dropped packets when the eval board works perfectly (see yesterdays post).

It's looking more and more likely that the receiver will need to be on a proper PCB. We always knew the transmitter would have to be completely fabbed from scratch as the strip board would be unsuitable. To be honest, once the board is printed, its a lot easier to work with a proper PCB - its just getting to that stage is not completely straightforward.

To make things just that a little bit harder, I'm going to be away from the middle of next week for a fair while. Andy doesn't return until after I leave which means virtually all the electronics work will come to a halt, at least for a few days. Hopefully I'll be able to get enough prepared so that he'll be able to continue with the radio fabbing whilst I'm away!

Troubleshooting: Day 2

The eval kit from Radiometrix arrived today allowing us to work out which board was faulty. It turns out that it is a problem with the receiver which means a more difficult diagnostic process. So far we have tested the Rx module, the IC and the power regulator - all which appear to be fine. I now suspect that the transistor that manages the RS232 to TTL conversion could be faulty - possibly heat damaged in the soldering process. We have learnt that it might be wise to load the Rx module in a SIL carrier - as its a real pain to keep re-soldering.

One bit of good news though - another range test was conducted using our transmitter on the breadboard and the eval receiver board. The transmitter was still inside our building and the helical antenna pointing horizontally rather than vertically. We were also in a highly urbanised area, which we knew would dramatically reduce range. In spite of all this we still managed to transmit an impressive 4500 feet. With so many improvements yet to be implemented (fabbed board, half wave dipole at transmitter end, elevated antenna, etc) we expect to be further impressed in future tests.

Troubleshooting: Day 1

Last night I noticed that the NBEK IC did not have a decoupling capacitor right next to it. Whilst there is one on the Vcc rail, it really is located too far away to be effective at controlling ripple. It was a long shot, but I thought this might actually cure the problem. It didn't.

We've also taken the null modem cable out of the equation as well as the RS232 to TTL converter on the transmitter side.

More kit allowing diagnostics turns up tomorrow.

Missing data

We've hit a snag... What had been working, now seems to have gone a little wrong.

We are currently investigating why we are losing data packets over the radio link. As yet we cannot be sure if this is due to a problem with transmitter or receiver. The only real change has been that the receiver is now a soldered circuit. This is a little unexpected as the fabbed board should make the receiver better, not worse. Another theory is that the transmitter is causing an issue due to it being on a breadboard either because of interference or inductance. Luckily Radiometrix have offered a loan of some evaluation kit which will pin down exactly where the problem is. Once we know which board has the problem we will know how to proceed.

Phil has bet on the receiver being faulty, whereas I think its going to be the transmitter. I hope I'm right as the fix will be simply to fab the board. If Phil happens to be right, that means we need to examine our finished receiver... not something we would want to dismantle!