Milligram scale?

I need to get something capable of measuring up to 10g in milligram increments.. Wondering what's available, Sparkfun didn't seem to have anything that small.

This project will be to size sunflower seed.. I will probably start just by weight, but eventually may add a camera to determine the area as well.. probably will be interfaced to an R-pi or PC for that kind of work.

Any pointers?

Hi, 1mg is 1/1000 of a gram. Your only solution is to research commercially available balances, laboratory quality with a PC interface.

Your biggest obstacle is signal noise from the loadcell array. It will also need a good mount to remove any vibration.

Tom.... :)

$11.62 with free shipping: http://www.ebay.com/itm/10g-0-001g-Digital-Electronic-Milligram-Precision-Scale-Gram-Jewelry-Diamond-YK-/152148675599 Probably not easy to interface but plenty cheap!

John, Yes, I was looking at those.. the interface is the problem though... guess I could get a couple an hack them, I'd probably eventually get it right.. I had bought some cheap plastic digital calipers that had a serial interface.. I was really hoping to find something similar for scales... Why can't this just be easy :)

For those sorts of devices the LCD hacking is probably the best bet. They normally have a SPI like interface and once yoi get it right can easily create a data dictionary.

A scope or logic analyzer would help... but if the data clock is slow an Arduino could be used to record the data going to the LCD as well.

Cheers

I was thinking perhaps intercepting the signal before the processor.. I would guess many of them have an amplifier like this http://www.ebay.com/itm/Electronic-Scale-Sensor-HX711-ADC-Bridge-Weighing-Anti-Jamming-For-Arduino-AVR-/171217937819?hash=item27dd62659b:g:7D8AAOxyRhBS1jDH, who's output could be tapped into.

All depends on the design of that particular scale I guess

This one is slightly cheaper: http://www.ebay.com/itm/Portable-20g-x-0-001g-LCD-Digital-Gram-Pocket-Diamond-Jewelry-Scale-Weight-Hot-/222185028280 $9.91 ($8.92+0.99 shipping)

musskopf: For those sorts of devices the LCD hacking is probably the best bet. They normally have a SPI like interface and once yoi get it right can easily create a data dictionary.

If you're going to do that, why not just point a camera at the display and read the numbers from the image?

odometer: If you're going to do that, why not just point a camera at the display and read the numbers from the image?

Because it requires several orders of magnitude more processing power and hardware?

Remember that those balances use the segment LCDs, not a graphic LCD, so the commands it's going to be sending to the screen will be fairly simple.

Google around about hacking cheap miligram scales - I wouldn't be surprised if they had (or some of them had) a serial output, like a lot of cheap chinese volt meters and calipers do.

Also - you know that those scales are not really accurate to 1mg right? They jump around by 5-6 mg at a time, not 1mg at a time (though removing weight and putting it back on helps - the digital stabilization that they use to hide the drift also ends up hiding the real signal). A scale that is good down to single digit mg is considerably more expensive, and less portable.

Also - you know that those scales are not really accurate to 1mg right?

For that price, you could get several scales and average the results to get more accurate weights!

(accuracy increases as sqrt(n) where n = number of scales).

It may be easier to use one of those cheap scales and just use the load sensors.

They can be expensive to mechanicaly design and implement, i have done this with commercialy available stuff and th mechanical arrangement is what costs.

The electronics required for load cells is well documented online.

Not seen a hack for an existing device but not been looking particularly.

If you look at my YouTube LoadCell videos #31 & #32 you will see I use a (max) 100g load cell which is very sensitive down to, I reckon, 0.3g without getting too affected by noise - that said, at that level the smallest breath on the sensor would set it off. And there was a 0.1g drift (probably temperature).

I don't know if you can get a 50g sensor (or less, see above posts) but if you can then this should be do-able. I measure from about 3g upwards for my particular Coffee Cup Coaster (yes, really, in daily use, works like a dream) so you never know what you can do until you just buy a sensor and have a go.

But don't go buying any 5Kg sensors and expect them to work, you want a really sensitive module, they must be available surely?

There's probably another techique that's useful for small masses, perhaps a small ampere-balance operating on a little see-saw with the sample on top of a small neodymium magnet - adjust and measure the current in a coil to restore equilibrium after adding the object to balance.

Only works for non-magnetic objects of course, and automating the balance would be a project (determining when its in perfect balance...).

If you want a scale which can measure in milligrams, then I'll help you. After research on the market, I've found some top rated measuring units which can give you an accurate result in milligram also.