RF testing across the pond

The "rotated antenna" mod to these RF modules greatly extends their range.





A few days ago we had a problem and the thing didn't even work 5 meters away. But passion and perfectionism win! Now the signal can reach the other side of a pond about 100 meters away.

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Current consumption

The current was measured through a 1-ohm resistor, therefore all readings in mV correspond to mA of current.

1. Listening. These values are a bit on the high side due to RF testing, they may come down by another 20-30%. Presently the ON time consumes 28.8mA for 6ms, which is equivalent to 0.000048 mAH. The cycle is repeated every 470ms. So every hour the device uses 0.367659mAh. That makes the 700mAh battery last 1904 hours or 79 days (2.6 months) when the device is never activated

2. The pager consumes an average of 20mA for 10ms each pulse, and the pager sound repeats this pulse 4 times. Therefore each pager activation uses up 20mA for 40ms. With one battery you could page 3,150,000 times without taking into account the listening overhead

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Waterproofing

It's waterproof. Done deal. You can put it in the washing machine for an hour. This is a big issue that's now 100% solved. Or shall we say 99%. More testing is needed just to ensure there is no variation across parts - but for now we're putting this aside until the new board design is sent out. We'll use the board creation time to do even more testing and make a video, no time so far.

Battery charging

After much seeking, there is no cheap battery charger that can take a lithium polymer cell with a connector and recharge it. The only stuff available is oriented towards RC hobbyists and is really overkill and costs a lot. Even if there was something like that on the market in China we can't sell it without paying several grands for testing it in the lab.

Therefore we can't order an off the shelf part. Also, li-poly cells can't be shipped in their charged state. So it seems we have to bite the bullet and do what we were trying to avoid, which is upgrade our remote to be able to recharge its own battery...

This is a lot of work and a lot more components. We're laying out the boards now hoping to get the RF issue and the charging straightened out in 1 trial and not waste any more time. We will also try to coerce the testing lab into including all this new circuitry in their original estimate.

Li-poly cells are hard to charge. There's a preconditioning phase, a fast charge phase, a constant voltage phase, and the battery absorption must be measured along with its temperature. There's an IC that does all this but it needs to be programmed carefully and it requires many external components.

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Motor trouble

Mr Tang's overmolded motors are worse than in previous trials - received 10 samples from him that are really poorly shaped, with pieces of rubber coming off, very ugly attachment, holes, and glue coming out. He's already wasted over 80 of our rare motors.

Immediately pinged Jason. We are ordering a mold to create small miniature metallic parts that will get spot welded onto the motors in order to stop using glue once and for all. This is our first mold to produce a metallic part. Theoretically we're already out of money but we can't go on wasting months this way, the manufacturing process needs to be repeatable!

The glue messes with silicone and screws up the curing process plus it introduces an amount of substance which has a different volume each time, molds don't like that. If Mr Tang still can't handle it we have Jason's word that we'll do this with someone else - honestly we hope he screws up again so we can get this done elsewhere, we've really had enough of trying and trying forever and spending months and wasting motors trying to get him to repeat a simple process! He's already managed to screw up with old expired rubber, with wrong hardness rubber, by changing glue when the old type was already working, and more. Sure, he's working a lot for us, but at the end of the day we have a product we need to ship and #1 is having good parts to build it.

So either way we're making the process a LOT simpler and also having a plan B in case he keeps making crappy parts. This is still good progress.

As for our other manufacturers, the LED guy won't return our money for the crappy parts he made which were already returned on his request. To make up for that we now have a GOOD battery supplier who can speak English, has supplied all safety testing documents, and isn't totally clueless like the guy we were using before. He told us very clearly the lithium polymer batteries will not create a fire even if shorted, much less explode. So we tried it (very carefully) and he was right, these batteries he sent us are totally safe even in worst case conditions.

Slowly we're forming a network of competent suppliers in all areas - sure we're having massive delays as usual, but the foundations are being built strong and sound.

RF Range panic and solution

Last week was the scariest and most complex since the project started. This post will try to put the fragments back together in a coherent fashion but time is scarce lately, we're working more than 12 hours a day and it's already 2am so don't expect clarity...

PART 1: The panic

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