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 by lyndon ¦  Sat Nov 22, 2008 3:17 pm ¦  Forum: SparkFun Product Questions ¦  Topic: First project - using a dial/knob? ¦  Replies: 12 ¦  Views: 1929

If the dial won't move when power is off, you can use a rotary encoder connected to a small (8-pin?) MCU with EEPROM and save state when the position is stable for 1 second. Since it's being used by hand, you're not likely to exceed the EEPROM max cycle time. Alternately, you can build a power-down ...

 by lyndon ¦  Sat Nov 15, 2008 5:55 pm ¦  Forum: New Product Ideas ¦  Topic: serial to 7-seg driver ¦  Replies: 4 ¦  Views: 1656

Those prices are pretty good. The people making them do have to eat, you know. And if Sparkfun were to resell them the price probably wouldn't be any less. macegr, Thanks for that list. While I would prefer something cheaper(individual 7-segs are just pennies apiece) i'd guess the r&d would add to t...

 by lyndon ¦  Sun Oct 26, 2008 2:13 pm ¦  Forum: SparkFun Product Questions ¦  Topic: Lateral Stabilization of a model glider ¦  Replies: 6 ¦  Views: 1471

IIRC, the guys at Rotomotion ( have open sourced their autopilot software and you can find it on Sourceforge along with hardware requirements. Theirs was for helicopters, but the basic principles are the same. This isn't easy to do and you'll probably have more success if you look...

 by lyndon ¦  Sun Oct 26, 2008 2:10 pm ¦  Forum: SparkFun Product Questions ¦  Topic: positioning and orientation sensor for small photo lights ¦  Replies: 5 ¦  Views: 1279

OK, I *have* to ask the obvious question. What's wrong with using three small angle protractors on each light and just writing it down after you take the shot? Low tech, no interference problems, no hardware/software to debug, no dead batteries, etc...

 by lyndon ¦  Tue Oct 21, 2008 9:23 am ¦  Forum: SparkFun Product Questions ¦  Topic: driving a mosfet from a logic level signal? ¦  Replies: 7 ¦  Views: 1801

I think a depletion mode FET will do what you need. But they can be hard to find in high-current models and you will need a negative voltage supply. Look at fig. 10 here: Alternately, can you use a NC relay? If you're only swi...

 by lyndon ¦  Tue Oct 21, 2008 9:16 am ¦  Forum: SparkFun Product Questions ¦  Topic: An efficient way to "roughly" regulate power? ¦  Replies: 9 ¦  Views: 1657

Have you looked for a small off-the-shelf DC-DC converter that can do what you need? As philba said, designing a 7A efficient switcher isn't trivial and it sounds like this is peripheral to your project, so you probably have better things to do with your time.

 by lyndon ¦  Sat Oct 18, 2008 10:01 am ¦  Forum: SparkFun Product Questions ¦  Topic: Battery Charging Circuit ¦  Replies: 10 ¦  Views: 1987

Can't you just use a comparator (with hysteresis) driving a FET to turn the current on/off? Alternately, if you don't want to deal with all that analog design, an 8-pin AVR and a TTL-level FET will do the same thing with a bit of firmware.

 by lyndon ¦  Sat Oct 18, 2008 2:16 am ¦  Forum: Wireless/RF ¦  Topic: Building a basic remote switch ¦  Replies: 10 ¦  Views: 1928

Part of the problem may be that you assume this is "really simple stuff...electronics 101." It isn't. Wireless radio communication is full of hidden complexity and trying to avoid that isn't going to get you far, which is why I offered the simple optical solution. OK, that won't work for your update...

 by lyndon ¦  Fri Oct 17, 2008 2:17 pm ¦  Forum: SparkFun Product Questions ¦  Topic: Nicad charging system help needed ¦  Replies: 6 ¦  Views: 1317

Nothing online, but I should still have the Eagle CAD schematics. I'll look around. Until then, here's what I remember: The charger was the Max712 design right out of the appnotes. It worked like a champ,: just had to adjust for the # of cells I was using. The discharger was a Proportional feedback ...

 by lyndon ¦  Thu Oct 16, 2008 7:23 pm ¦  Forum: Wireless/RF ¦  Topic: Building a basic remote switch ¦  Replies: 10 ¦  Views: 1928

If it''s just across a single room, I'd think of using optics before RF. Just like your TV remote control. Generating the signal is trivial and you can purchase the Sharp remote control receivers all over the place: Sparkfun may even have them.

 by lyndon ¦  Thu Oct 16, 2008 7:17 pm ¦  Forum: SparkFun Product Questions ¦  Topic: Nicad charging system help needed ¦  Replies: 6 ¦  Views: 1317

Hah! That's funny: I built exactly that system using a MAX712 for the charger about 3 years ago. Discharge current was up to 30A -- fried a bunch of power resistors & FETs until I got it right :-)

Not much to it: about $15 in parts IIRC.

 by lyndon ¦  Fri Oct 03, 2008 6:03 pm ¦  Forum: New Product Ideas ¦  Topic: Track sheep! ¦  Replies: 19 ¦  Views: 6301

Interesting idea. Is there any reason you're not using a sheepdog? I also live on a farm ( -- we have chickens and horses) and I have the same thoughts. It's like a second job and anything you can do to save time is worthwhile. However, sometimes the old ways w...

 by lyndon ¦  Sat Sep 27, 2008 6:36 am ¦  Forum: New Product Ideas ¦  Topic: Easy Pneumatics? ¦  Replies: 2 ¦  Views: 1307

What are you working on? I have some pneumatic stuff, but I don't do much with it.

Bluetooth range?

 by lyndon ¦  Tue Sep 23, 2008 10:20 am ¦  Forum: Wireless/RF ¦  Topic: Bluetooth range? ¦  Replies: 1 ¦  Views: 780

What range are you guys getting with your Bluetooth modules? Using the built in Bluetooth in a Thinkpad and my RN41 I can't get anywhere near the quoted 300 ft. even line of sight in clear air. I think my best so far is about 100' I could go to ZigBee, but I guess I'd like to be sure that I'll get s...

 by lyndon ¦  Mon Sep 15, 2008 3:13 pm ¦  Forum: SparkFun Product Questions ¦  Topic: Simple on/off dectection via bluetooth? ¦  Replies: 10 ¦  Views: 1641

I think what Mike meant was that the USB device may need to be setup every time it powers on. The price differential between a USB Bluetooth transceiver and one of the modules from SparkFun is minimal. I picked up a Targus USB dongle at OfficeMax for $39 and the SparkFun RN41 Bluetooth serial module...

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