For quite a while I used the Plaato Keg scales in my kegerator. For the most part, I really liked them. Unfortunately, they recently announced that they were killing off the API that I used to get information about my keg levels. I also spoke with a friend of mine that said he was looking for a solution, but had trouble finding something that was low enough profile. I decided it was time to replace the Plaato Kegs and create something as low profile as possible. What I ended up with was a scale that can support a full keg and is only 13mm in height which is actually thinner than the Plaato Keg. These are also quite a bit cheaper than the Plaato Keg and clock in at just over $260 for the whole setup if done as a single set, compared to about $100 per scale for Plaatos.
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There are two main components to this. The scales, and the controller. The controller is powered via an ESP32, specifically, an esp32-s3-devkitc-1-n8r2. The controller (as built) supports 5 scales (4 kegs + CO2 tank), a drain sensor, and a pressure sensor.
You will need the following tools to assemble the scales and controller as detailed.
- 2.5mm Hex Allen Key
- T20 Torx Bit
- #1 Phillips Screwdriver
- Soldering Iron
- Terminal Crimping Tools
- M3x0.5mm Tap
- M4x0.7mm Tap
You will also need access to a 3D printer (or someone with one) that has a build plate capable of printing a 190x210mm object to build the enclosure. An alternative is to purchase an enclosure from your local big box store and modify it as required.
The quantities of parts listed below is for 4 keg scales and the controller. It does not include the pressure senor or load cell for the CO2 tank, however, if you want to utilize one of these scales for your CO2 tank, you just need to add those parts. The STLs that are part of this repo make use of the parts listed below. Changing parts may require you to modify the STLs accordingly.
| Part | Part Number | Qty Needed | Used For | Approx Unit Cost | Subtotal |
|---|---|---|---|---|---|
| Meanwell 25W 5v Power Supply | RS-25-5 | 1 | Controller | 12.73 | 12.73 |
| C-13 Fused Power Inlet | FN9260SB-2-06-30 | 1 | Controller | 14.48 | 14.48 |
| #6 Crimp Fork Terminals | generic | 5 | Controller | 9.94 | 9.94 |
| 14ga Female Spade Connector | varies | 3 | Controller | - | - |
| ESP32 S3 DevKitC 1 | ESP32-S3-DevKitC-1-N8R2 | 1 | Controller | 5.96 | 5.96 |
| Prototype Board | generic | 1 | Controller | 8.49 | 8.49 |
| Molex SL 4 Circuit Panel Mount Housing | 70107-5038 | 5 | Controller | 0.85 | 4.25 |
| Molex SL 3 Circuit Panel Mount Housing | 70107-5037 | 1 | Controller | 1.39 | 1.39 |
| Molex SL 2 Circuit Panel Mount Housing | 70107-5036 | 1 | Controller | 1.23 | 1.23 |
| Molex SL 4 Circuit WireToWire Housing | 70107-0003 | 4 | Cables | 0.45 | 1.80 |
| Molex SL 4 Circuit Plug | 70066-0388 | 8 | Cables, Scales | 0.32 | 2.56 |
| Molex SL 22-30ga Crimp Socket | 16-02-0069 | 50 | Cables, Scales | 0.08 | 4.00 |
| Molex SL 22-30ga Crimp Pin | 16-02-0105 | 50 | Controller, Cables | 0.09 | 4.50 |
| Molex 4P TPA | 73838-0004 | 17 | Controller, Cables, Scales | 0.20 | 3.40 |
| Molex 3P TPA | 73838-003 | 1 | Controller | 0.17 | 0.17 |
| Molex 2P TPA | 73838-002 | 1 | Controller | 0.24 | 0.24 |
| Harwin M20 22-30ga Crimp Terminals | M20-1180046 | 30 | Controller | 0.09 | 2.70 |
| Harwin M20 Polarising Key | M20-003 | 5 | Controller | 0.28 | 1.4 |
| Harwin M20 1pos Housing | M20-1060100 | 1 | Controller | 0.12 | 0.12 |
| Harwin M20 2pos Housing | M20-1060200 | 2 | Controller | 0.13 | 0.13 |
| Harwin M20 4pos Housing | M20-1060400 | 5 | Controller | 0.20 | 1.00 |
| Harwin M20 5pos Housing | M20-1060500 | 1 | Controller | 0.24 | 0.24 |
| Harwin M20 6pos Housing | M20-1060600 | 5 | Controller | 0.28 | 1.40 |
| Harwin M20 10pos DR Housing | M20-1070500 | 5 | Controller | 0.41 | 2.05 |
| Harwin M20 22pos Socket | M20-7822046 | 2 | Controller | 2.20 | 4.40 |
| Harwin M20 8pos Header | M20-9730846 | 1 | Controller | 0.35 | 0.35 |
| Harwin M20 4pos Header | M20-9730446 | 1 | Controller | 0.19 | 0.19 |
| Harwin M20 2pos Header | M20-9730246 | 6 | Controller | 0.10 | 0.60 |
| Harwin M20 4pos DR Header | M20-9720246 | 1 | Controller | 0.25 | 0.25 |
| Scale Tops from Send-Cut-Send | 0.125" 304 Stainless Steel | 4 | Scales | 27.45 | 109.80 |
| M3x0.5x05mm SHCS | 91292A123 | 4 (Sold in packs of 100) | Controller | 8.18 | 8.18 |
| M3x0.5x5mm SHCS | 91292A110 | 32 (Sold in packs of 100) | Scales | 6.00 | 6.00 |
| M4x0.7x10mm BHCS | 90991A122 | 4 (Sold in packs of 100) | Scales | 6.64 | 6.64 |
| M3x0.5x4mm Heat Insert | generic | 4 | Controller | 9.39 | 9.39 |
| 28ga 4 pair Silicone Wire | generic | 1 | Cables | 19.98 | 19.98 |
| 50kg Load Cells | generic | 1 | Controller, Scales | 9.99 | 9.99 |
| Extra HX711 | generic | 1 | Controller | 9.49 | 9.49 |
| Subtotal: | $269.44 |
Note
Some of these items have volume discounts that may not be reflected in the above list. For the Harwin M20 connectors, people may opt to use generic dupont clones that you can find on any mass retail site. Using generic connectors can bring your costs down a little bit and give you plenty of spares, however I personaly prefer to get genuine parts when I can. I do not recommend that you purchase the Meanwell power supply or power inlet off of Amazon due to the high rate of fakes. The ones that I've seen sell for pretty much the same price, so it's best to get those from a reputable source like Digikey or Mouser. You can get a large pack of screws from Amazon as well. I find the socket formation on their screws to be a bit suspect at times, but they should suffice for our purposes.
If you can find other people that want scales, your per-part price from Send-Cut-Send can come down considerably. For example, when going from 4 scales to 8, the unit price drops by $4 to 23.29. The more people you get in on the purchase, the cheaper the indiviual pieces will be and you can split up some of the bulk items like screws and such. Another alternative is to 3D print scale tops. For my prototype, I printed a 6MM thick plate out of ABS. It held up perfectly fine with a standard corny keg. Using 3D printed scale tops can drop your per-scale cost down to almost nothing and really bring the project cost down. Plastic does flex though, so I cannot say how a 3D printed top might hold up over the long run.
For the controller, you'll first need to print out the top and one of the bottoms. For the top, I recommend supports for the recessed area for the USB ports. Everything else can be printed without supports. I printed my cases with Polymaker PolyLite Silver PETG.
- Solder the headers onto your ESP32. You'll want to solder the headers to the back side of the ESP32.
- Solder the two Harwin M20 22-position sockets (M20-7822046) on the Back of the breadboard. Viewing the above picture, the front has individual solder points as opposed to joined traces. Be sure that the right side of the board indicates negative as our wiring assumes the far right pin will be ground. It can be helpful for soldering to insert your ESP32 into the sockets before soldering the sockets to the board to help hold them in alignment. You sockets should be soldered into holes A7-28 and I7-28.
- To the front, headers as shown in the Header Locations.
- Add a jumper wire from F8 to the + rail and from I28 to the - rail.
- Once complete, it should look something like the following:
- Next, wire the ESP32 to the HX711s and then the HX711s to the panel mount connectors. They should be wired up similar to how is illustrated in the Scale Wiring, however there's no guarantee that the HX711's that you get will have the same pinout so be sure to wire them appropriately. From the HX711s to the panel mount SL connectors, use the six position M20 connector to join the A and B channels (+ to +, - to -). This will allow you to select any gain level without re-wiring the connectors. A channel supports a gain of 128 or 64. B channel supports 32. A lower gain decreases the sensitivity of the scales which can be helpful if there's too much variation or noise.
- I had SendCutSend produce my scale tops. You can use the 9in Scale Platform file to get a set. I did not have them tap the holes, but you may opt to have them do so. I went with 1/8" Stainless Steel for mine. Another option is to print a set of tops. If you opt to print a set of tops, you'll need to use M3x4x5mm heat inserts which are not included in the BoM. I recommend ABS.
- If you opted for the SendCutSend plates and did not also opt for the tapping service, you will need to tap each of the holes with M3 or M4 taps. Each top should have 8 M3 threaded holes, and a single M4 threaded hole.
- Next, print (or get printed) 8 each of the Sensor Mount and Sensor Support as well as 4 of the Support Legs.
- When opening the load cells, they should be paired and have similar numbers written on them. Be sure to keep the paired cells together for each scale. For each cell, create a sandwich with the mount, the cell, and the support. Attach it to the scale top with the M3 screws.
- For wiring, crimp together the White and Black of opposite cells to a single pin. This should result in four pins for the SL connector. Pin 1 (Cell 1 White, Cell 2 Black), Pin 2 (Cell 1 Black, Cell 2 White), Pin 3 (Cell 1 Red), and Pin 4 (Cell 2 Red). Pin 1 will be your E+, Pin 2 is E-, Pin 3 to A+, and Pin 4 to A-.
- Attach the support leg to the top with one of the M4 screws. Use a small zip-tie to secure the wires from the load cells. Don't pull them fully tight.
There's a few "phases" to get the device up and running with Home Assistant.
-
In Home Assistant, go to Settings -> Devices & Services -> Helpers
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Create the Helpers for the following:
- Keg 1 Tare (kg)
- Keg 2 Tare (kg)
- Keg 3 Tare (kg)
- Keg 4 Tare (kg)
-
Make sure ESPHome is installed and working.
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Using a paperclip or something similar, depress the boot button on the ESP32 and hold it while it's plugged into the computer.
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From the ESPHome add a New Device. ESPHome should detect the device type automatically.
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In the YAML editor, update the first few lines to be as follows
esphome: name: <device-name> friendly_name: <Device Friendly Name> on_boot: priority: -100.0 then: - light.turn_on: id: onboard_led brightness: 100% red: 0% green: 100% blue: 0% transition_length: 0s - delay: 2s - light.turn_off: onboard_led esp32: board: esp32-s3-devkitc-1 variant: ESP32S3 framework: type: esp-idf psram: mode: quad speed: 80MHz
The important part is to update the framework to use esp-idf instead of arduino.
Caution
Note, that the above assumes that the board is the exact same one in the BoM. If it's different, confirm the settings and adjust as nessecary. The psram section may need to be altered or ommitted entirely.
-
Upload the first batch of firmware and make sure the device returns logs.
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Edit the yaml again and add the following after the
captive_portal:section.time: - platform: homeassistant id: update_timer on_time: - seconds: 0,10,20,30,40,50 minutes: /1 then: - light.turn_on: id: onboard_led brightness: 100% red: 0% green: 0% blue: 100% transition_length: 0s - component.update: scale_one_raw - light.turn_off: onboard_led - seconds: 2,12,22,32,42,52 minutes: /1 then: - light.turn_on: id: onboard_led brightness: 100% red: 0% green: 0% blue: 100% transition_length: 0s - component.update: scale_two_raw - light.turn_off: onboard_led - seconds: 4,14,24,34,44,54 minutes: /1 then: - light.turn_on: id: onboard_led brightness: 100% red: 0% green: 0% blue: 100% transition_length: 0s - component.update: scale_three_raw - light.turn_off: onboard_led - seconds: 6,16,26,36,46,56 minutes: /1 then: - light.turn_on: id: onboard_led brightness: 100% red: 0% green: 0% blue: 100% transition_length: 0s - component.update: scale_four_raw - light.turn_off: onboard_led - seconds: 8,18,28,38,48,58 minutes: /1 then: - light.turn_on: id: onboard_led brightness: 100% red: 0% green: 0% blue: 100% transition_length: 0s - component.update: scale_co2_raw - light.turn_off: onboard_led light: - platform: esp32_rmt_led_strip rgb_order: GRB pin: 48 num_leds: 1 rmt_channel: 0 chipset: WS2812 name: "Onboard LED" id: onboard_led ##################### # Beer Drain Sensor # ##################### binary_sensor: - platform: gpio pin: number: 9 inverted: true mode: input: true pullup: true id: beer_drain_full name: "Beer Drain Full" ############################### # Scales and Pressure Sensors # ############################### sensor: ###################### # Diagnostic Sensors # ###################### - platform: wifi_signal name: "WiFi Signal dB" id: wifi_signal_db update_interval: 60s entity_category: "diagnostic" unit_of_measurement: dBm - platform: copy source_id: wifi_signal_db name: "WiFi Signal Strength" id: wifi_signal_strength filters: - lambda: return (((90.0 - abs(x)) / 60.0) * 100.0); unit_of_measurement: "Signal %" entity_category: "diagnostic" ######### # Keg 1 # ######### - platform: homeassistant entity_id: input_number.keg_1_tare_kg id: keg_1_tare_kg name: "Keg 1 Tare (Kg)" internal: True accuracy_decimals: 3 - platform: hx711 clk_pin: 5 dout_pin: 4 gain: 64 filters: - median: window_size: 3 send_every: 3 send_first_at: 3 id: scale_one_raw update_interval: never name: "Scale One Raw" - platform: copy source_id: scale_one_raw unit_of_measurement: kg filters: - calibrate_linear: - 49135 -> 0.0 - -83849 -> 10.002 - lambda: return x - id(keg_1_tare_kg).state; accuracy_decimals: 2 id: scale_one_kg name: "Scale One Kg" - platform: copy source_id: scale_one_kg unit_of_measurement: Oz filters: - multiply: 33.814 id: scale_one_oz name: "Scale One Remaining Beer (Oz)" ######### # Keg 2 # ######### - platform: homeassistant entity_id: input_number.keg_2_tare_kg id: keg_2_tare_kg name: "Keg 2 Tare (Kg)" internal: True accuracy_decimals: 3 - platform: hx711 clk_pin: 7 dout_pin: 6 gain: 64 filters: - median: window_size: 3 send_every: 3 send_first_at: 3 id: scale_two_raw update_interval: never name: "Scale Two Raw" - platform: copy source_id: scale_two_raw unit_of_measurement: kg filters: - calibrate_linear: - -33834 -> 0.0 - 115053 -> 10.002 - lambda: return x - id(keg_2_tare_kg).state; accuracy_decimals: 2 id: scale_two_kg name: "Scale Two Kg" - platform: copy source_id: scale_two_kg unit_of_measurement: Oz filters: - multiply: 33.814 id: scale_two_oz name: "Scale Two Remaining Beer (Oz)" ######### # Keg 3 # ######### - platform: homeassistant entity_id: input_number.keg_3_tare_kg id: keg_3_tare_kg name: "Keg 3 Tare (Kg)" internal: True accuracy_decimals: 3 - platform: hx711 clk_pin: 16 dout_pin: 15 gain: 64 filters: - median: window_size: 3 send_every: 3 send_first_at: 3 id: scale_three_raw update_interval: never name: "Scale Three Raw" - platform: copy source_id: scale_three_raw unit_of_measurement: kg filters: - calibrate_linear: - 281137 -> 0.0 - 425363 -> 10.002 - lambda: return x - id(keg_3_tare_kg).state; accuracy_decimals: 2 id: scale_three_kg name: "Scale Three Kg" - platform: copy source_id: scale_three_kg unit_of_measurement: Oz filters: - multiply: 33.814 id: scale_three_oz name: "Scale Three Remaining Beer (Oz)" ######### # Keg 4 # ######### - platform: homeassistant entity_id: input_number.keg_4_tare_kg id: keg_4_tare_kg name: "Keg 4 Tare (Kg)" internal: True accuracy_decimals: 3 - platform: hx711 clk_pin: 18 dout_pin: 17 gain: 64 filters: - median: window_size: 3 send_every: 3 send_first_at: 3 id: scale_four_raw update_interval: never name: "Scale Four Raw" - platform: copy source_id: scale_four_raw unit_of_measurement: kg filters: - calibrate_linear: - -140124 -> 0.0 - -286031 -> 10.002 - lambda: return x - id(keg_4_tare_kg).state; accuracy_decimals: 2 id: scale_four_kg name: "Scale Four Kg" - platform: copy source_id: scale_four_kg unit_of_measurement: Oz filters: - multiply: 33.814 id: scale_four_oz name: "Scale Four Remaining Beer (Oz)"
Note
You can name the helpers in step 2 whatever you like. Be sure to update the yaml file with the correct device id of the helpers that you create.
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Upload the new firmware and watch the logs. The scales should all be connected and should start reporting values.
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Allow each sensor to rest for a bit with no weight on the scale. Go to Settings -> Devices -> ESPHome -> . View the raw values for each scale and note the current values. Depending on the gain, you may need to take a median or average of a few readings.
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Add a known weight onto one of the scales and let it rest for 15-20 minutes. This will allow enough datapoints to account for noise. I used 10kg for mine. A full keg would be even better so that we can calibrate both ends of the measurement range. Regardless, ensure you know the weight of the object on the scale down to at least 0.02kg. This level of precision will allow us to measure roughly a one ounce pour.
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Once values for zero and the known weight for each scale has been obtained, go back and edit the yaml. Update the
scale_x_kgfilters with the new raw values and expected values.filters: - calibrate_linear: - 49135 -> 0.0 - -83849 -> 10.002
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The scales should be all set and can be used to build dashboards
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They can also now be used to feed other things such as live updating tap handles:
