Simple wall-mounted weather station

Anonymous 06 Feb 2022 17:09 12 7455 Cool? (+19)

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TL;DR

A wall-mounted weather station uses DS18B20, BMP180, and DHT11 sensors in a KM-111 enclosure to show indoor and outdoor temperature, pressure, and humidity.
The design prioritizes readability over graphics, with a simple LCD display, no trends, no screen-clearing flicker, and an Arduino mix of prefabs and custom code.
BMP180 pressure needed a 1.013 correction factor, and comparisons with METAR reports showed about 1 hPa error above 1000 hPa and 1-2 hPa below it.
Both thermometers read practically identically, but the cheapest blue LCD modules refresh sluggishly, taking up to a second.

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I liked the Byrrt weather station Link So I decided to create my own, simpler and stupider version on the commonly available and cheap DS18B20, BMP180 and DHT11 sensors (but with a housing). I aimed at the readability of the information on the display, so there are no infographics, no "trends", etc. Indoor and outdoor temperature, pressure, humidity and that's it.

Software is an arduin conglomerate of prefabs and custom scribbles. The program correctly displays negative temperatures, there are no double minus flowers between -9 and -10 degrees, I did not use the "lcd_clear" command, so the screen does not blink. For reasons unknown to me, the pressure measurement with the BMP180 had to be multiplied by 1.013 for the result to be correct, I connected another sensor, but it turned out to be damaged. For a few days I compared the accuracy of the pressure measurement with the METAR reports from a nearby airport, above 1000 hPa the error did not exceed 1 hPa, below 1000 hPa the indications differed by 1-2 hPa, it is difficult, I will live with it. The indications of both thermometers are practically identical.

The board is dual-voltage, so you can use various modules, not only at 5V, in the presented project the BMP sensor is powered by 3.3V, but you can solder the LM78L05 there and it will also work. The analog part is filtered with a simple 10 uH filter, I didn't give any quartz capacitors, because I didn't, but there is room for them. The presented version is a wall-mounted device, although the design of the housing is a matter for the user and it may as well be free-standing, etc. outside the device.

The housing is KM-111 from the Maszczyk offer. A little warning against the cheapest blue LCD displays, the characters are not displayed, just "displayed" at a sluggish pace. The refresh time is in practice up to a second.

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pier 07 Feb 2022 07:59

Hi With pressure measurement you are fine. The sensor simply measures absolute pressure and the pressure above sea level is commonly used. Check with this calculator if it is correct. If you want,... [Read more]

Tomekob 07 Feb 2022 08:46

"pier", but you made me happy with this calculator, I needed it and I didn't know it was and where. THANKS! [Read more]

ArturAVS 07 Feb 2022 09:18

Minimalistic workmanship and good functionality, a big plus from me. Very good selection of electronics housing. [Read more]

efi222 07 Feb 2022 10:25

As my colleague @pier noticed, the DHT11 is a toy, although you can find a good one. As for the BMP180, they have factory spreads of up to 3 hPa. And here only a software correction can help. Make the... [Read more]

Slawek K. 07 Feb 2022 19:28

Such a small note, the station does not measure the temperature in the room (room), but the temperature of the electronics inside the housing. The sensor should be placed outside, at the bottom of the... [Read more]

Anonymous 07 Feb 2022 20:17

None of that, all the thermometers are on the outside, only the humidity is measured inside. You can see it in the last photos. [Read more]

Slawek K. 08 Feb 2022 02:00

You write about the DS18B20, which I see on the board, and the DHT and BME sensors are on the outside of the board, but still inside the housing. I don't know which sensor you are taking the temperature... [Read more]

Anonymous 08 Feb 2022 08:39

Believe me they are not :) The device is wall mounted, but this "wall" is a plate with a hole underneath (old wardrobe), so the sensors are on wires outside the casing (and also outside the wardrobe).... [Read more]

pier 08 Feb 2022 08:50

Oh, the BMP180 will not measure the pressure correctly, how will it be in the housing? As for DHT11 I already wrote, it does not measure moisture. [Read more]

Anonymous 08 Feb 2022 08:55

Some kind of festival of misunderstanding begins. In addition to pressure, the BMP180 also measures the temperature inside, so it cannot be in the housing, and the Dallas is supposed to be outside (because... [Read more]

pier 08 Feb 2022 09:02

It's cool, I forgot about the temperature measured by BMP, but I won't let DHT go away, it's crap. And how do you tend to calculate the NPM pressure as I wrote? [Read more]

Slawek K. 08 Feb 2022 11:47

In an earlier post you wrote that I should look at the photo, the photos show where the sensors are, so I wrote my comments on this basis. If you wrote in the description that the sensors are on the wires,... [Read more]

FAQ

TL;DR: A dual-voltage Arduino weather station shows ±1 hPa above 1000 hPa after a 1.013 software factor [Elektroda, Anonymous, post #19868303] "DHT11 is crap" [Elektroda, pier, post #19871413] Use sea-level correction and place sensors outside the case for believable data.

Why it matters: Calibrated hobby sensors can rival airport METAR reports for day-to-day forecasting.

Quick Facts

• BMP180 absolute pressure accuracy: ±1 hPa typical, ±3 hPa max (300–1100 hPa) ["BMP180 Datasheet"]. • DS18B20 temperature accuracy: ±0.5 °C from −10 °C to +85 °C ["DS18B20 Datasheet"]. • DHT11 humidity accuracy: ±5 % RH within 20–90 % RH ["DHT11 Datasheet"]. • KM-111 ABS enclosure size 110 × 60 × 30 mm, cost ≈ €3 [Maszczyk Catalogue, 2022]. • 16×2 blue LCD refresh time 0.5–1 s [Elektroda, Anonymous, post #19868303]

How do I convert BMP180 absolute pressure to sea-level (QNH) pressure?

Use the barometric formula: P₀ = Pabs / (1 – h/44330)⁵·²⁵, where h is elevation in metres. Insert outdoor temperature for higher accuracy. Elevation 200 m shifts readings by ≈24 hPa [Elektroda, pier, post #19869291]

Why did the author multiply BMP180 readings by 1.013?

Their sensor showed 1.3 % low. Multiplying by 1.013 aligned values with nearby airport METAR; error stayed <1 hPa above 1000 hPa [Elektroda, Anonymous, post #19868303]

What accuracy can I really expect from BMP180?

Factory spread is up to 3 hPa across the range [Elektroda, efi222, post #19869486] Typical units stay within ±1 hPa after one-point calibration ["BMP180 Datasheet"].

Is the DHT11 suitable for reliable humidity readings?

No. Forum testers call it “random values” [Elektroda, pier, post #19869291] Datasheet lists ±5 % RH, but the sensor drifts and freezes above 80 % RH—an edge case that wrecks long-term logs ["DHT11 Datasheet"].

Where should I place the temperature sensors?

Mount DS18B20 and BMP180 outside the enclosure bottom so electronics heat does not bias readings [Elektroda, Slawek K., post #19870491] Keep them shaded from sun and rain.

Can one PCB support both 3.3 V and 5 V modules?

Yes. The author used a dual-voltage board; 3.3 V feeds BMP180, while an optional LM78L05 can provide regulated 5 V for other parts [Elektroda, Anonymous, post #19868303]

Which housing fits this simple station?

A Maszczyk KM-111 ABS box was chosen for wall mounting; it costs about €3 and drills cleanly for a 16×2 LCD window [Maszczyk Catalogue, 2022].

How do I stop a 16×2 LCD from flickering during updates?

Avoid lcd.clear() calls; update only changed characters. This keeps the screen steady and refresh under one second [Elektroda, Anonymous, post #19868303]

What cable length can DS18B20 handle?

With 5 V power and a 4.7 kΩ pull-up, the sensor works over 100 m of CAT5e routinely [Maxim, 2015].

How do I add software pressure calibration?

Log airport QNH, sensor absolute pressure, and outdoor temperature.
Compute correction factor: Factor = QNH / Pabs.
Multiply future readings by Factor inside loop(). This three-step method reduced error below 1 hPa in the thread station [Elektroda, Anonymous, post #19868303]

What happens if DHT11 faces saturated humidity?

Above ≈80 % RH the polymer capacitor swells; output locks at 99 % until dried, creating multi-hour data gaps ["DHT11 Datasheet"].

Can I replace DHT11 with a better sensor?

Yes. Pin-compatible DHT22 offers ±2 % RH and −40 °C operation for under €5; or switch to Bosch BME280 for combined T/RH/P logging via I²C [Bosch, 2018].

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