Pressensor mode for the Half Decent Scale

Your Half Decent Scale can now talk to the Pressensor directly. No phone, no app: pressure, weight, flow rate and a self-starting shot timer, all on the scale's own display.

Mid-shot: 9.2 bar, 36.4 g in the cup, 2.1 g/s, 19 seconds. The line across the middle is a live 0–12 bar pressure gauge.

Pressensor mode is part of the official Half Decent Scale firmware, published by Decent Espresso as an approved plugin. It is free and open source, and it works with every Pressensor.

What you need

Item	Notes
Half Decent Scale	Decent Espresso's open-source scale. Tested on V8 hardware.
Pressensor	Mounted on your machine as usual. Nothing about the sensor changes.
A computer	Chrome or Edge, plus a USB data cable for the scale. The firmware is built online, so no developer tools are needed.

1. Build your firmware

Decent's build page assembles a firmware image with the Pressensor plugin included. Pressensor needs no WiFi and no extra features — it speaks Bluetooth, which is always present.

Open the HDS Custom Build page

Under Firmware version, choose main. The plugin is published for main, so it stays hidden if you pick an older release.
Leave Features untouched unless you want them for other reasons, such as WiFi updates.
Under Approved plugins, tick Pressensor.
Press Request build and keep the page open. The status moves from Queued to Building to Ready.
Download HDS_FW_custom.zip and unzip it.

The plugin list on the build page. Illustration, not a screenshot.

2. Flash the scale

Connect the scale to your computer with the USB cable and open the WebSerial ESPTool in Chrome or Edge. Connect to the scale, then write the four files from the archive at these addresses:

File	Address
`bootloader.bin`	`0x0000`
`partitions.bin`	`0x8000`
`firmware.bin`	`0x10000`
`littlefs.bin`	`0x670000`

You may need to press the reset button on the scale's circuit board before the tool can see it. When flashing finishes the scale reboots and behaves exactly as before — weighing, timer, app connection — until you switch the new mode on.

A full flash erases the scale's stored settings. Afterwards run Calibration → Calibrate from the scale's setup menu before trusting a weight. If you are already on recent firmware and only want to add the plugin, write only firmware.bin to 0x10000 with esptool instead — that leaves your calibration untouched.

3. Pair your Pressensor

The Pressensor is discoverable whenever a battery is fitted, so there is nothing to switch on or wake up.

Switch the scale off, then hold both buttons while switching it on to enter the setup menu.
Step with ◯ to Pressensor and select it with ◻.
Choose Pressensor On, then Select Sensor. The scale scans for five seconds and lists every sensor nearby, strongest signal first.
Pick yours, then Back and Exit.

Your choice is saved permanently. From then on the scale reconnects to that sensor by itself, every time it starts.

4. Reading the screen

The display is divided into four quarters:

①Pressure in bar, top left, straight from the sensor. ②Weight in grams, top right. Tare any time with ◯. ③Flow rate in g/s, bottom left. While idle this quarter shows the status instead: armed, connecting, no sensor, or the result of the last shot. ④Shot timer, bottom right. —The divider across the middle fills from left to right as a 0–12 bar pressure gauge. •The dot in the corner shows the sensor link: filled means live data, hollow means connecting.

Armed and waiting. Weigh your beans freely — weight never starts the timer.

Shot finished: 36.2 g in 31 seconds, 9.4 bar peak.

5. Pulling a shot

Put your cup on the scale, tare, and start the extraction. You do not need to touch the scale again.

Moment	What happens
Pressure passes 1 bar	The timer starts on its own. It re-arms only after pressure has dropped back down, so leftover pressure cannot start a second shot.
Espresso flows	Weight and flow rate update live, and the gauge follows the pressure curve.
Flow dies away	Once at least 8 g has landed in the cup and flow stays low for three seconds, the shot ends. The time is taken from the last real flow, so trailing drips do not stretch your shot time.
Finished	The timer freezes and the peak pressure appears. Press ◻ to reset for the next one.

The scale measures your yield from the moment the shot starts, so the automatic stop works even if you forget to tare. The weight shown on screen is always the true weight on the platform, so tare before the shot if you want to read the yield directly.

Flushing costs you nothing. A flush briefly crosses the start threshold, but a shot that ends quickly without ever building real pressure cancels itself and the timer returns to zero. No cup needed.

If you prefer full control, switch Auto Start off in the menu and run the timer yourself with ◻: press to start, press to stop, press to reset. Auto Stop can be turned off separately.

Troubleshooting

What you see	What to do
Pressensor is missing from the plugin list	Check the firmware version on the build page. The plugin is published for `main`, so it is hidden when an older release is selected.
Status stays on `connecting`	The scale keeps retrying by itself. Check that the sensor has a working battery and is within range, and that it is not already connected to your phone or another device.
Status shows `no sensor`	No sensor has been saved yet. Run Select Sensor from the menu.
Pressure is slightly off at rest	Use Zero Sensor in the menu while the machine is idle. The scale also zeroes the sensor once each time it powers up and connects.
The timer did not start by itself	Auto Start may be off, the sensor may not be streaming (check the dot), or the pressure never dropped low enough to re-arm after the previous shot.
You want the normal scale back	Choose Pressensor Off. The standard weighing screen returns immediately.

One habit worth keeping: tare before the shot, not during it. While the shot runs, the scale is measuring your drink.

Pressensor mode is part of the open-source Half Decent Scale firmware (GPLv3).

Country/region