livestock weigh scales

Tool Concept
Stage: 
Ready to Build

 

License:
Description: 
A cattle farmer occasionally needs to weigh his animals, but weigh scales for cattle are expensive to purchase for the small operator ($1,000 to $1,500 or more). This is an accurate electronic scale you can make yourself for about $500.
josefo's picture
Hi, not sure if you are still around since this post is almost 3 years old but ill aska nyway, Im trying to build this for my calves as well. Im testing it and trying to "calibrate" it, however, Im not getting stable results for example, after I zero the board and wait some 10 to 20 minutes the values fluctuate a bit as usual but instead of getting -1, -2, 3,, 0,1 etc (around zero) I start to get 9, 10, 8, 10, 11, 7, ... or shifting to around -4: -3,-5,2, -1, 0, etc,... this makes calibration very difficult because Im not sure if the zero has shifted up and down as Im weighing things... My question is, do you think the power suppply voltage has anything to do with this fluctuation? Im using two 9 volt batteries in series, 180 ohm resistors (changed the formula accordingly) and I got the dwyer 626 with less error than the 628, any suggestions or tips are welcome!
Documentation
Documentation Wiki: 

Functional Description

This livestock/cattle weigh scale uses pressure transducers to read the hydraulic fluid pressure in hydraulic rams under each corner of the weigh deck. Pressure is converted to force, and some basic statistical stuff is calculated and the resulting weight of the animal is wirelessly transmitted to the receiver which may be in sight outside the corral or in hand of a helper.

How to use the tool

Arrange a site for the scale supports so that the weigh deck is level and does not rock on the four hydraulic rams. You might want to pour small concrete pads for this purpose. Place the transmitter (wired to the pressure transducers via RCA connections) under the deck to protect it. Turn on transmitter and receiver and zero the deck (i.e. account for tare weight). Expect results to fluctuate just a few pounds based on the accuracy of your pressure transducers.

Materials and sourcing (main and non-obvious materials)

  • Dwyer Series 628CR pressure transducers - four (one for each corner). Note that accuracy is stated in terms of "full scale" (FS). Example, a 500 psi transducer with 1% accuracy at FS has +/- 5 psi anywhere in that pressure range, so it is to your advantage to use the smallest pressure rating needed. This example used 500 psi which certainly works but is too conservative. The transducers are the largest single expense.
  • Short body hydraulic ram from Harbor Freight, part no. 95979 This is sort of like a bottle jack. They are very short with a hydraulic piston that extends only 7/16 inch.
  • moteino R4 This is an wireless arduino type board from http://www.lowpowerlab.com
  • the weigh deck consists of two layers of 21/32 in. (or thicker) 6 x 2 ft. plywood, anti-skid surface/material on top for hooves, and 3 x 2 x 3/16 in. angle bolted on sides for reinforcement
  • two 2-ft. long sections of channel beam (as shown in images) or other suitable material to secure the hydraulic rams. Try a scrap steel yard.
  • standoff screws to secure the printed circuit board (PCB) to the project box. So, select a PCB with pre-drilled standoff holes.
  • small sheet of clear plastic (like for a picture frame) as a cover for the receiver box so you can see the display
  • project box such as Cantex (Item #: 10029 | Model #: L5133709 at Lowes) "new work wall electrical box" or similar (e.g. Carlon) without any pre-made holes or outlets.
  • RCA connectors
  • tip: you will be looking for "panel mount" buttons, switches, RCA plugs, etc. to interface into the plastic project box
  • See notes on the circuit diagrams for additional electronic parts and sources, etc.

Construction, how-to build

  • Construct the deck as described and shown in the images.
  • Remove the fittings that came with the hydraulic rams. Fully extend the ram piston using an air nozzle pressed into the hole. Then back off the piston 1/16 inch to allow for thermal expansion, etc. Fill each ram with hydraulic oil without any bubbles. A syringe with large gauge needle may be used. The recommended pressure transducers have the correct thread size to screw into the hydraulic rams. Use plumber's teflon tape.
  • build the transmit and receiver boxes as shown in the images
  • build the circuit boards as shown in the images
  • program the moteinos in the transmit and receiver boxes: see post at https://lowpowerlab.com/forum/index.php/topic,782.0.html The code seems to be more properly formated there (Markdown syntax was not too clean here)
    • The hardware and microcontroller programs should be considered opensource.

TRANSMITTER CODE

RECEIVER CODE

pattycoole's picture
Hi Trenton, are you still involved with this site? I saw some of your posts and wanted to ask if you had followed up on any of your other proposed projects. I will be building a set of these scales! I was wondering if I would be able to do the build with different transducers to the ones you used? Looks like there are some much cheaper options available.
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