Communication device for autistic children - Page 1
Forum section: electronics / projects

author: embeddedcake
author_rank: Newbie
timestamp: April 16, 2025, 04:14:03 pm
content: Hey everybody!I am working on a project and need help choosing the right parts and procedures.The project goes as follows:- There should be a "main"-computer running a local webserver.- There should be up to 8 different "remote"-devices. A remote should:- Remotely communicate any button-press to main (I expect there to be only 4 buttons)- Be powered externally- Use as little power as possible.- Go into sleep mode after some time without activity.- It is not expected for a remote to be turned on for more than 60 minutes per day.- The setup should be plug-and-play. Once main and the (necessary amount of) remotes are turned on, they should set up the communication automatically.My questions are the following:1. What parts should I use? I am an amateur so it's important for me to use parts that are beginner friendly and flexible, even if they cost much more.2. How should a remote communicate with main, ensuring a plug-and-play behavior and low power consumption?3. How do I power the remotes externally effectively and **safely**.I tried to answer these questions myself. Here are my ideas:1. What parts should I use?: For main I plan on using a Raspberry Pi 4. For the remotes I thought about using an ESP32 with a built-in voltage regulator. Im not sure if im missing on other crucial parts besides the buttons, a 3D-printed casing and other miscellaneous parts.2. How should a remote communicate with main, ensuring a plug-and-play behavior and low power consumption?: I have two ideas:1. Have the remotes connect to main automatically via Bluetooth-Low-Energy. As I have no prior experience using BLE, I am not sure if it will work out to connect 8 devices to the Pi 4 this way.2. Have the remotes connect to the local network via WiFi and interact directly with the web-server that way. The problem here is that I'm not sure how power efficient this will be and I'd need to find a way for the remotes to get the network credentials dynamically. Maybe from main with BLE?3. How do I power the remotes externally effectively and **safely**: It is of the utmost priority for this to be safe and in the best case also easy to install. My idea here is to connect a 9V battery to the remote directly. Therefore I'd use an ESP32 with a built-in voltage regulator. Does that make sense? Do you expect it to work?If you can spare some time to lend me your expertise I'd be very grateful. This project should help autistic children communicate more effectivly.

author: PGPG
author_rank: Frequent Contributor
timestamp: April 16, 2025, 05:45:38 pm
content: Until I came to reading about Bluetooth I was sure that you are writing about devices connected with cables.We are doing the hand-held RFID reader you can see here:https://micromade.pl/produkty/bibinet-m/czytniki-m/bibi-r54/It is powered with 3 x AA cells. Device consumes 0mA (nothing is working there) until you press the button. Then it runs its RFID reader and communicates by ZigBee with base station. You can select recorded passage (normal/service entrance/exit) by next button presses. If 10s nothing happens it switches itself completely off.Feedback from users says that they have to change batteries typically once per 3 months. I suppose they register several dozen people entering/leaving by cars every working day.RFID reader need much more current than your buttons (buttons can consume 0mA until are pressed).I have no practical knowledge about power needed for radio communication. We used ZigBee as it is much, much slower than Bluetooth or Wifi so should need much less power.

author: daqq
author_rank: Super Contributor
timestamp: April 16, 2025, 05:48:23 pm
content: First of, thank you for your noble goal.Quote from: embeddedcake on April 16, 2025, 04:14:03 pmThe built in voltage regulators on most cheap devboards are linear regulators, therefore they are very inefficient. This goes against your 'low power consumption' requirement. Very simplified, it just 'chops off' the extra voltage, while using the same current. So to get +3.3V from +9V, you have an efficiency of some ~40%. Compare that with the most basic switch regulator and that gives you some 80-90% efficiency.That said, using a 9V battery that is not rechargable will get pretty expensive or at least annoying, unless you do a good job on trimming the power consumption. There's nothing preventing you from using rechargeable cells. NiMH are extremely forgiving and can take some very crude charging practices, with even chargers for them being easy to design. Lithium batteries provide more energy per volume/mass, but are far less forgiving when it comes to charging. I mean, they are in everything, and work completely fine in the 99.999% of cases, but if you really want to go for safety and replacability of the batteries, NiMH are a good choice.QuoteWi-Fi is a power hog. Definitely BLE is the way to go. ESP32 is also a power hog, but less so when using BLE. There are MCUs that are not as popular (for hobbyists), but have better power consumptions and BLE - see stuff from Nordic semi.Concerning how many devices you can have connected, not sure, but I believe 8 is doable.QuoteThe choice of Raspi as the 'master' box is good I think. The ESP32, see above.

author: PGPG
author_rank: Frequent Contributor
timestamp: April 16, 2025, 06:26:25 pm
content: Quote from: daqq on April 16, 2025, 05:48:23 pmEverything depends.To reduce power consumption (12V supply, 5V needed) I have used linear LDO (XC6216D502PR) with its supply current 5uA. Supplied device was most time sleeping needing 10uA. So I got 15uA current consumption with efficiency only 28% (=5*10/12*15).I was doing it 20 years ago. DCDC efficiency drops down when your current need is very little and I don't know if even nowadays you can reach better result using DCDC. Those time I didn't even considered DCDC because of being more expensive.If the device to be designed will have no switch-on, but have to be in some stand-by state to be able to read button pressed all the time (and then activate) than long battery life can be reached by minimizing current consumption when nothing happens (sleep modes). If you reach very low supply current needed than DCDC self consumed current can make it being worse solution than linear regulator.

author: sheikhshuhad
author_rank: Newbie
timestamp: July 01, 2025, 10:52:39 am
content: For Bluetooth low energy part i would suggest try BleuIO. The AT commands available on the device is really helpful to build on any platform.https://www.bleuio.com/