Connecting a load cell to the spark core

I have just receivd my spark core + a small digital scale i ordered from ebay(which i loved tearing appart down to its electronics).
My basic goal is just to get a read from the scale to the spark app.

I only have little knowledge on cuircuits and programming but hopefully with your help i might be able to make it happen.

All i know about the scale is that it’s range is 1gr-5kg and work on two 1.5 volt battery. I understood i need an amplifier. how do i choose the right one? What are the calculations i need to do?
Do i need any other resistors/capacitors in my cuircit? if so, why? and how do i choose one?

Any help will be really appreciated…
Thank you so very much.


Your load cell looks like it is a 4 wire bridge. RED and BLACK are likely to be the supply to the bridge and WHITE and BLUE are the sense output.

[EDIT] HAH… Even better. I zoomed in your image and the wires are nicely marked for you. E+ and E- is the supply or excitation for the bridge and S+ and S- are the sense outputs.

If you get yourself a multi-meter you can power it up and check the red and black wires to see that they are using.

The blue and white will be in the mV range so you will need to build an instrumentation amplifier to bump up the signal to suit the ADC input on the core.

That white gunk on the load cell is to protect and secure the wiring and the strain sensor itself so take care with that part.

Cool project though so good luck with it and post your progress.


Thank you for your help dave!

What are the statistics im looking for in the load cell’s and amplifier’s data sheet, so i can do the right calculations (i dont know what they are…) and see that they are right for each other? and to the spark of course :smile:

thank you!

This might be useful, since the arduino and Spark are rather similar: as far as I’m aware, the Spark can tolerate 5V as input, like the arduino. This would mean you could use the same (or similar) amplifier.


If I remember correctly, I think a handful of GPIOs are not 5v tolerant, handy list here:


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Dave, you’re rght. I only remembered there were some tolerant ones.
Seeing as those are digital pins only, the voltage has to be upped to a maximum of 3.3V. The gain of the amplifier is set by the resistor, so by changing that value, you should be able to make it work with < 3.3V. The calculations for that are in the datasheet. You don’t actually have to use that specific amplifier, just something that boosts your signal to a readable level. You’ll have to calibrate it yourself anyway.


I really appreciate your help guys.
Thanks again.