cheap electronic compass

oem_odm · Nov 19, 2009

**broken link removed**

hi everyone

please see the image below in reference to a cheap compass. I'm not an electronic engineer so pls bear in mind

the idea is to create cheapest form of electronic compass. it will be in-accurate by about 15degrees, slower than gyro ones, and need to be held flat like a compass. Whats wanted is cheap + general direction according to 8 co-ordinates.

just like with normal compass, its bar rotates on a pin. the bar is fixed to a black card (thin, light, black about 200gr/gsm card). A slot in the card to allow IR light to pass through for the photo interuptors. depending on the cards rotated position, 1 or 2 photo interupters would be postive (passing IR light through the slot. With each photo interupter connected to an MCU pin each, could calculate the position......

right?

Menticol · Nov 19, 2009

Awesome draeing, are you a designer?

birdman0_o · Nov 19, 2009

Ya, what software made that drawing?

oem_odm · Nov 20, 2009

funny, not quite the feedback i was looking for chaps. it's solidworks + touch of photoshop.

Any feedback on the actual post would be very cool

blueroomelectronics · Nov 20, 2009

Electronic compasses are not very expensive for low resolution models, are you planning to mass produce your design? What would be the need for a low resolution compass? What product(s) do you envision could use it?

oem_odm · Nov 20, 2009

hi blueroom

could you recommend some cheap electronic compasses and sources? - similiar to what I've envisaged.

(mass production is in mind - a robot application)

thanks

blueroomelectronics · Nov 20, 2009

Try digikey search for compass, in quantity these are cheap.
Honeywell HMC6042-TR is $6.5 ea @ 2k

oem_odm · Nov 20, 2009

thanks bill.

i saw the honeywell one - gave up after couldnt find pricing. You gonna think im a scrooge - my version would cost about a dollar i think including an MCU.

waiting for pricing from these guys:

**broken link removed** (MDSM-1000A/B could be ok)

blueroomelectronics · Nov 20, 2009

How are you going to keep your robot level and still while you take compass readings with your original design?

oem_odm · Nov 20, 2009

as long as its level within 12 degrees, should be fine. it doesn't move that much im changing the above design, replacing single hole on card with slots which will be counted - just need figure out a way to calcualte direction using photodiodes

blueroomelectronics · Nov 20, 2009

Another problem is the compass needle will only block the light when it's directly over the optical sensor. 99% of the directions will show nothing. Add the time & cost of a DIY design to the price of a modern 2 or 3 axis chip ~$30 and the chip will be cheaper.

oem_odm · Nov 20, 2009

i see your point. the card will have holes round its edge. those holes depending on the position of the needle will allow/block the optical sensors.

Jirka46 · Nov 30, 2009

oem_odm said:
i see your point. the card will have holes round its edge. those holes depending on the position of the needle will allow/block the optical sensors.

If you used Grey code wheel printed on the bottom of your card and reflective sensors, you would get 16 positions with just four sensors and each additional sensor would double number of them. Also it would be easier and cheaper to make than cutting holes or slot.

Jirka

See this
Optical Encoder Wheel Generator

Vizier87 · Dec 1, 2009

try KMZ51 / KMZ52 as well. They're also cheap.

oem_odm · Dec 4, 2009

Jirka46 said:
If you used Grey code wheel printed on the bottom of your card and reflective sensors, you would get 16 positions with just four sensors and each additional sensor would double number of them. Also it would be easier and cheaper to make than cutting holes or slot.

Jirka

See this
Optical Encoder Wheel Generator

hi jirka, great reply thanks....would you mind doing me a drawing of some sort so i could understand you better? (think your idea is great)

oem_odm · Dec 4, 2009

Vizier87 said:
try KMZ51 / KMZ52 as well. They're also cheap.

hi Vizier87 - how cheap are these?

Jirka46 · Dec 5, 2009

oem_odm said:
hi jirka, great reply thanks....would you mind doing me a drawing of some sort so i could understand you better? (think your idea is great)

Hi, the picture shows what I meant. The encoding disc would be printed on paper and glued to the bottom of blue disk. Four sensors would read it. You would have to decode grey code to binary in your MCU.
Jirka

Vizier87 · Dec 5, 2009

oem_odm said:
hi Vizier87 - how cheap are these?

They're solid state compass, which means they don't use mechanical motion of the needles or anything, but rather it uses the relation between earth's magnetic field through Hall effect and voltage as output.

See http://www.datasheetcatalog.org/datasheet/philips/KMZ51_3.pdf

they cost around $4.70 USD at digikey.com

oem_odm · Dec 10, 2009

Hi Jirka,

Yes i see your idea. It's good. You mount all the sensors on the same tangent line.

thanks for your input

oem_odm · Dec 10, 2009

Vizier87 said:
They're solid state compass, which means they don't use mechanical motion of the needles or anything, but rather it uses the relation between earth's magnetic field through Hall effect and voltage as output.

See http://www.datasheetcatalog.org/datasheet/philips/KMZ51_3.pdf

they cost around $4.70 USD at digikey.com

Hi Vizier, thats great. Thankyou very much

cheap electronic compass

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