Useful 0.50" x 0.75" circuit ?

Bean

I just got a bunch of 1225 coin cells from ebay, and I wanted to make a really small circuit with them.
The SMT holder is 0.50" x 0.75" so that is how big I want the circuit board to be.
The coin cell holder will be on one side, so the circuit must fit on one side of it.

I know I could do some kind of LED flasher or something. But I though I would see if you guys had any good ideas.

The cells only have about 30mAH capacity so the circuit can't use alot of power.

Oh they are 3V also.

I'd like to make something using the SX20AC/SS, it fits easily with a good bit of room to spare.

Any ideas ?

Bean.


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Phil Pilgrim (PhiPi)

With a wire antenna on one of the SX20 pins and a temperature sensor, you could send the temp in Morse code on an AM broadcast frequency.

-Phil

D Faust

How about one of those cricket, chirper things?

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--DFaust

Phil Pilgrim (PhiPi)

If you do the chirper, add a couple wires you could stick in the soil next to a houseplant to measure the resistance. Chirp when it needs watering.

-Phil

Bean

Phil,
I guess using the internal 4MHz clock is out of the question for transmit to an AM radio ?
100 on the AM dial is 1MHz right ? Since a jump takes 3 cycles I don't see how I could generate a 1MHz clock ?
I could do it with the SX48 hardware timers. I guess I could use the SX48, it's alot harder to mount though...


P.S. Anyone know of any really small switches ?

Bean.

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Post Edited (Bean (Hitt Consulting)) : 10/29/2007 2:14:21 AM GMT

Phil Pilgrim (PhiPi)

Switches: pushbutton, toggle, or solid state?

BTW, 5-, 6-, or even 7-cycle loops will put you in the AM band.

-P.

Post Edited (Phil Pilgrim (PhiPi)) : 10/29/2007 4:39:24 AM GMT

Brian Carpenter

this is a new approach. I dont think that i have ever heard anyone start with a board size and say, ok what should i make?

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It's Only A Stupid Question If You Have Not Googled It First!!

Phil Pilgrim (PhiPi)

I think it's a pretty cool idea. It's like haiku in a way: restrict your form to the bare minimum and see where creativity can take you.

-Phil

uxorious

What about just making it a key part of a circuit. In other words, make your board the main board for the SX, required circuitry for it to run (and be programmed), and some way to connect to it (header of some sort?). Then, if I want a temp sensor circuit that sends data on a one wire interface I build that part of the circuit on another board with a mating connector and attach it to your board? Almost like a miniature version of the SX proto board.

Also, if you are having PCBs made, make them round like the coin cell. That will give you a little more real estate to play with.

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~~ dRu ~~

Sparks-R-Fun

I am all for data logging! Give me an SX, an EEPROM, maybe even a real-time clock and one or more ADC channels. Then make it Prop-Clip compatible (unless you really do not want the circuit board to stick out that far beyond the battery holder) so that I can download data from it and possibly adjust its settings.

Temperature and light intensity should be fairly easy to implement. If you can throw soil moisture content in there as well you might have a really useful product!

- Sparks

D Faust

Prop Clip + SX?

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--DFaust

metron9

I bought a water filter that came with a little device that has a push button. Push it and it starts blinking 6 months later. Seems silly at the time but so far that thing has gon off 3 times now!

i thought a tiny little blinker that you could push a button the number of days before it went off could be used for food in the fridge. Push three times for three days when it starts blinking it's time for leftovers or its time to throw it away!

Since you can put the processor to sleep (well i don't know about the SX20 but with an atmel chip you could run it for years on that tiny battery.

I just ordered 250 .575 x .575 boards that have·4 components on it. A resistor, a·PTC fuse a TVS diode and a 6 to 12V dc/dc regulator that takes a 6V car voltage and runs a 12 volt tachometer gauge. Attached is the board.

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Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!

Post Edited (metron9) : 10/30/2007 3:35:57 AM GMT

Dennis Ferron

Why don't you put a 2-axis acelerometer on the board and a ring of LED's all the way around so that when you tip the disk, it makes it look like the light "pools" in the side that is angled down?

Bean

All good ideas guys.

Problem is alot of sensors either won't work from 3V or need a regulated voltage to get stables readings (analog).

I an get the SX20, Sx-Key header, Prop clip/USB2SER header, 256KB EEPROM, RTC but then I'm out of room. I think I'm going to get rid of the RTC and just run the SX from a xtal to have good time-keeping. But then what to log ?

I'm still thinking about the AM radio transmission idea too. Phil, I guess you mean that because a square wave has lots of odd harmonics, if I generate a 333.33KHz square wave there will be enough 1MHz energy to hear on the AM radio. Is that what you meant ?

D Faust, the Prop clip is just used as a serial interface to retreive the data (not to program the SX). At least that is what I assumed Sparks meant.

Bean.

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Post Edited (Bean (Hitt Consulting)) : 10/30/2007 4:38:52 PM GMT

D Faust

Thanks for clearing that up.

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--DFaust

Sparks-R-Fun

D Faust said...
Prop Clip + SX?

Bean said...
D Faust, the Prop clip is just used as a serial interface to retrieve the data (not to program the SX). At least that is what I assumed Sparks meant.

Yes. I was suggesting the use of a Prop-Clip as a small footprint way to exchange data with the device. I was also thinking one Prop-Clip could be used to support many of whatever tiny device Bean devises by connecting them one at a time as necessary. This would save space on the circuit board by not requiring each device to have its own communication circuitry and significantly reduce the cost for supporting multiple devices as well.


Bean,

If you are not familiar with the SHT1 temperature and humidity sensor from Sensirion, I recommend requesting a free sample. I received mine today and it is small. I would say it is about half the size of the SX48. I have a remote data-logging project in mind for it.

If it works well, I will probably be ordering more of them. Then again, if you are going to design a drop-and-retrieve type device with temperature, humidity and light level recordings I might just let you do all the hard work!

Keep us posted.

- Sparks

uxorious

The SHT11 will run off of 3volts. (2.4-5.5 per spec) and gives you temp and humidity. That would be a great candidate, except they are not cheap ($23 for the device only at Newark or $29.95 for Parallax's setup). The package size is very small and difficult for most to solder, so buying the part alone isn't always an option.

For other sensors, you can try using a voltage booster. They come in SOT23-6 packages and only require a small amount of support components. At work, we have a product that uses a 12 volt sensor from a 2xAA source. It uses a Maxim MAX8570 LCD Boost device and works extremely well. The schematic for that part of the circuit is attached. The green line in the upper left is the 12v output. VCC is 3v (2xAA)

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~~ dRu ~~

Bean

Well here is my first attempt. It's meant to have LEDs connected to the pads, but you could connect anything.

It can be programmed using the 4 holes near the corners.

Because these boards will NOT have solder mask, it really limits what you can do on the bottom without the battery shorting things out.

Bean.


Post Edited By Moderator (Chris Savage (Parallax)) : 11/2/2007 3:41:53 PM GMT

Bean

Okay I finally got the PCBs made for my RSC (really small circuit).
There are pads for Batt+, Gnd, and 4 I/O pins (with series resistors).

So now I ask everyone "What can I do with it ?".

Any Ideas ?

Right now it just flashes two red leds. But it has been flashing them for over 16 hours straight now!
There are four vias for Vdd, Vss, OSC1 and OSC2 to program it.

Bean.

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Post Edited (Bean (Hitt Consulting)) : 11/9/2007 7:00:01 PM GMT

Tracy Allen

Hi Terry
I use a plastic tape from the Brother labelmaker between the battery and the PCB, with a hole punched in the center. A low mound of solder on the center pad then makes connection with the battery, and the tape insulates any necessary thru-holes (which you assiduously avoided!). The label on the end has a diagram for how to install the battery (in case one forgets!). I've never done a 1225 battery, only big by comparison 2032.

I was wondering about the circuit in the recent board. The two leds are unipolar, yes, but the unstuffed center pad looks like it could accommodate a bicolor led, if you can find one with two terminals. Most of the bicolor SMD leds seem to be in three or 4 terminal packages. Why 100ohm resistors in series with both legs? It wil certainly make a good refrigerator magnet or tie clasp.

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Tracy Allen
www.emesystems.com

Bean

Tracy,
Good idea with the label maker. I'll have to try that.

The pads and series resistors are just generic, I put LEDs on two pins just to play with it.

Yeah a tie clasp.....Now what would be a cool thing to do with it as a tie clasp... Hmmmm

Bean.

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