Build your own Digital Scale with this DIY Kit

Electronics DIY kits are easy to find from either Arduino kits, or robotics kits, to oscilloscope kits among others. But I can’t remember ever seeing digital scale kits, maybe because I did not look for it, but that’s exactly what I found on ICstation for $27.99 with a scale that can measure weights up to 10 kilograms with a reported one gram accuracy. The DIY scale can also be pruchased on eBay for $29.99.

Main items in the (Trans–CRS–162DZC) kit and features:

  • MCU – STC MCU Limited STC89C52 8-bit (80C51 compatible) MCU in 40-pin DIP package
  • RTC – DS1302 8-pin DIP chip + CR1220 socket and battery
  • EEPROM – AT24C02 serial EEPROM (DIP chip)
  • Display – LCD1602 16×2 digit display
  • Keypad – 4×4 matrix keypad
  • Sensors – DS18B20 one-wire temperature sensor, “C3 high precision” 10kg strain pressure sensor
  • Boards – HX711 load cell amplifier module, printed circuit board for the MCU, RTC, EEPROM, etc…
  • Misc – Buzzer, transistors, various passive components
  • Enclosure and accessories
  • Power Supply – 5V DC
  • Dimensions – 15.2cm x  14.1cm x 6.5cm (assembled)
  • Weight – 500 grams

Follow the assembly guide to build the scale yourself, and you should be good to good to use your own scale/clock/alarm/thermometer toy.The scale could also be the starting point to make your own design either programming the STC89C52 micro-controller with your own program (AFAIK source code is not available so you’d have to start from scratch), or possibly “IoTize” the scale by replacing the MCU by a Bluetooth or WiFi (ESP8266) module.

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guzman
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guzman

Amazing DIY kit with some real purpose, especially if combined with esp8266 for example for reporting weight readings to cloud

gicho
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gicho

I think “10 kilograms with a reported one gram accuracy” is more likely to be “one gram resolution”.

theguyuk
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theguyuk

Now if they made it programmable, you could have postal scales the tell you the price by weight and size?

Occam
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Occam

What? Using any one of many modern flash micros the design could eliminate, clock chip, eeprom and temp sensor

Drone
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Drone

@gicho
You said, ‘I think “10 kilograms with a reported one gram accuracy” is more likely to be “one gram resolution”.’

It may not achieve “10 kilograms with a reported one gram accuracy”, but if it is designed with reasonable care it should get fairly close. For example, a single load-point cantilever shear-beam load cell (like the one used in the scale shown here) should be capable of an OIML Type-C3 total error of +/-0.02% of rated load. At 10 Kg that comes to +/-2g.

Significantly better results are possible with calibration and/or temperature compensation. Remember, that’s just the load cell error. You’ve still got errors in the electronics, especially the load cell instrumentation (differential) amplifier and power supply. But again, with reasonable care, the error from the electronics should be quite small.

Also, never choose a load cell range that is wider than you need, that degrades total accuracy. I would prefer a 10X more accurate 1 Kg scale kit over the 10 Kg version and use a separate off-the-shelf inexpensive kitchen scale for loads over 1 Kg.

I’m not comfortable with what looks like plastic construction in this scale, especially at loads of 10 Kg. Weigh scales are like milling machines, rigidity is king. Any sort of unwanted bending moment is a potential source of error.

An error budget and analysis for any metrology project is a prerequisite to ever picking up a screw-driver or a soldering iron. But we rarely see it in projects/products like this. That’s not good.

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