New project support - Page 1
Forum section: electronics / beginners

author: Fionn
author_rank: Contributor
timestamp: July 06, 2025, 05:53:18 am
content: I would like to ask on some help to get started on a small project.I would like to make a temperature/Humidity sensor (lets call the whole assembly a "module") with its own rechargeable battery. Display and case are not needed for the module(s). It will communicate to the Receiver via lora as I learned its a very good option for that. The module should update and send info every 60-120 seconds to the Receiver that is a Raspberry Pi 4b (presumably with a SX1262 LoRa HAT) which logs the data to a file/sql/whatever. The 60-120 seconds are only interesting for the battery size calculation as I would like to have a big enough battery that needs Recharge no more than +- every 6 Months. It needs a small red led to warn as soon as the battery is low OR if its feasible send a msg to the central unit that its getting low (in this case no led), or maybe send it with every report - the point is to have some level of battery reporting.I'm aware that there are off-the-shelf ready to use modules like this:https://mydevices.com/product/dragino-lht65n-lorawan-temperature-humidity-sensor/but 1st of all this is way to overpriced for 62 Yankee bucks + 75 shipping + VAT = more than 150$ and I would like to do it myself at least to some degree at least - meaning connect the parts (maybe even create my own pcb (done that many many years ago)), program it, 3d print a case, make an grafana or similar reporting diagram, and so on.What I don't have:good English knowledge - sorry. Its very hard to get all the datasheets and understand them as wellElectronic engineering background, but have IT engineeringBatteryUSB-C connectorLora module for the sensor unit (and antenna)Temp/Hum sensorsany smd partWaveshare SX1262 LoRa HAT for Raspberry Pi (868MHz - EU)(That should be the easy part:https://www.aliexpress.com/item/1005004373257238.html)What I have:EnthusiasmPRi4bLEDsAssortment of resistors (good general coverage)Soldering stuff1-2 breadboard + wires + digital power supply + misc stuffI have asked the AIs and got the following suggestions:Searched around and found those as well (to my surprise seems not to be hallucination) so I added the links.LoRa Module RFM95W-868S2https://www.aliexpress.com/item/1005002404709432.htmlTemp Sensor SHT31-D I2C digital temperature & humidity sensorhttps://www.aliexpress.com/item/32695064184.htmlBattery 3.7V 6600mAh Li-ion Rechargeable, USB-C chargeablehttps://www.aliexpress.com/item/32942281148.htmlBattery Charger TP4056 USB-C With protection circuithttps://www.aliexpress.com/item/1005007593596607.htmlMCU Arduino Pro Mini 3.3V Ultra-low power microcontrollerhttps://www.aliexpress.com/item/1005006072999395.htmlMisc. PCB, headers, resistors, LED For assembly and battery warning $5.00Got also those funny pictures:But at the end of the day it confused me even moreWhat I would like to achieve in the 1st place to have a working prototype on a breadboard where I may connect the of shelf parts (like the lora to the sensor and batt and so on) without blowing up everything.The programming part is not that interesting as of now.And I know I may sound selfish/stupid but for a small project like this I'm not ready to go to the deepest holes of EE. I rather give up on the idea as I have only limited time and budget to spend.Are the suggested parts enough to achieve my goal or is there something missing?Thanks for the inputs!

author: ledtester
author_rank: Super Contributor
timestamp: July 06, 2025, 07:57:07 am
content: Quote from: Fionn on July 06, 2025, 05:53:18 amThe battery power requirement is the most challenging aspect of this project.Where exactly are you going to put this device? How far away will it be from an AC wall outlet?It's one thing if this device is going to be placed in the middle of the woods. But if it just going to be in your backyard then there be other ways to get the temp and humidity data to a device that can get it to the Raspberry Pi.

author: Fionn
author_rank: Contributor
timestamp: July 06, 2025, 08:03:24 am
content: This will be inside (and 1-2 outside) the house. In 99% of the cases there is no power supply available next to it (attic/basement/catio/etc). The Rpi will have its own power suppy rather in the center of the house and the most distant device would be like 25-30m away with a few walls (stone/concrete) in-between.

author: ledtester
author_rank: Super Contributor
timestamp: July 06, 2025, 08:25:06 am
content: Some options are:- a BLE device like as described here:https://hackaday.com/2020/11/17/custom-firmware-for-cheap-bluetooth-thermometers/- a wireless sensor that uses the ISM band like this:https://www.amazon.com/Crosse-Technology-TX141TH-BV4-Thermo-Hygrometer-Transmitting/dp/B0BLX7RQRG/Theses devices usually transmit at 433 MHz and you can receive and decode their signals using a SDR dongle like this:https://www.aliexpress.us/item/3256803734279374.htmlThese kinds of wireless temp sensors have been around a long time so you might find used ones at what we call a "thrift store".Both devices should run for a long time on their designed battery but you can always substitute a larger capacity pack that is rechargeable.

author: ledtester
author_rank: Super Contributor
timestamp: July 06, 2025, 08:34:33 am
content: Here's a video on using a SDR dongle to decode 433 MHz transmissions:How To Decode 433Mhz Low Power Devices Using RTL433 And A RTL-SDR Receiverhttps://youtu.be/JdzVIjKA68o

author: Fionn
author_rank: Contributor
timestamp: July 06, 2025, 10:13:35 am
content: Quote from: ledtester on July 06, 2025, 08:25:06 amThanks for the optionsUnfortunate but the LYWSD03MMC is now 20$ (EU) for 2 however this has 2-3 issues for me:- Missing the DIY part- The shipped meter may have new protections in place / new version and I may need to wait a long time till he finds a new way to update, and I'm sure they will not tell what version they ship. Still impressive what he has done on the video- Its using BLE which I don't want (nor WiFi)X141TH-BV4 is not available in the EU and is also quite pricey. Found as example thehttps://lilygo.cc/products/lora3?variant=51248229548213which is nice but also again missing the DIY part (and also 20$+vat+20$ shipping + batt)In opposite the linked parts in my opening post are around 10$ for each module including battery (and shipping) so I rather would go that route.

author: ledtester
author_rank: Super Contributor
timestamp: July 06, 2025, 03:33:07 pm
content: Another option is to use Zigbee.. see attached pics for more info.You will need a Zigbee receiver for your PC which serves the same purpose as the SX1262 LoRa HAT you mentioned.

author: madires
author_rank: Super Contributor
timestamp: July 06, 2025, 04:25:18 pm
content: You can get inexpensive weather stations (around 20 bucks) with outdoor sensors (temperature, humidity, ISM band transmitter, sometimes with a small LCD). Usually they support up to four sensors (ID switch in the sensor). The outdoor sensor would need only a charging circuit and the receiver in the indoor/display unit could be used for the RasPi. There should be plenty of documentation about the protocols. And the readily available outdoor sensors would give a reasonable battery runtime.

author: Fionn
author_rank: Contributor
timestamp: July 06, 2025, 05:18:11 pm
content: Thanks for all the suggestions, but all those miss the point of the DIY aspect of the receiver.

author: floobydust
author_rank: Super Contributor
timestamp: July 06, 2025, 06:58:27 pm
content: Heltecis low cost and has good ESP32 + Lora modules. The components you would need, for a prototype as well.Lots for sale atAliexpress Heltec productsmany have an OLED for development work.

author: Fionn
author_rank: Contributor
timestamp: July 06, 2025, 07:34:54 pm
content: Quote from: floobydust on July 06, 2025, 06:58:27 pmThank you. This (example:https://www.aliexpress.com/item/1005009128793055.html?) would than if I got you correctly replace theLoRa Module RFM95W-868S2 and the MCU Arduino Pro Mini 3.3V Ultra-low power microcontroller?

author: ledtester
author_rank: Super Contributor
timestamp: July 07, 2025, 02:26:12 am
content: Quote from: Fionn on July 06, 2025, 05:53:18 amOne thing the AIs didn't mention is that you'll also need a USB-to-TTL converter to program the Pro Micro. And it will need to output 3.3V signals.Given your situation I would second floobydust's suggestion of using the Heltec module.Here's a video from a Hungarian youtuber on the using the Heltec ESP32/Lora module:ESP32 LoRA with the Heltec WiFi LoRa 32(V3)https://youtu.be/7BlPcQgJay8

author: Terry Bites
author_rank: Super Contributor
timestamp: July 08, 2025, 12:49:55 pm
content: https://www.aliexpress.com/item/1005008550134548.html?spm=a2g0o.productlist.main.5.740f5bac33EK9A&algo_pvid=c6052069-a343-4068-8ead-c51cc139cc4f&algo_exp_id=c6052069-a343-4068-8ead-c51cc139cc4f-4&pdp_ext_f=%7B%22order%22%3A%22630%22%2C%22eval%22%3A%221%22%7D&pdp_npi=4%40dis%21GBP%213.71%213.39%21%21%214.91%214.49%21%40211b612517519789601641739e4afd%2112000045704380867%21sea%21UK%213100120370%21X&curPageLogUid=mErTMCv8kwUo&utparam-url=scene%3Asearch%7Cquery_from%3A