My prototype using a LAN cable breakout enclosure made it small and nifty.
A few years ago while using many wireless systems on a large remote property I had the problem of testing the signals in varies areas before installing my hardware like: Roboguards or my own custom devices that have the ability to communicate with the RoboGuard ecosystem.
Front view of the PCB. It fits perfectly into an ABS enclosure.
So I decided to create a dedicated remote that uses the ASK protocol used with these devices. This makes my life so much easier because it allows me to test multiple requirements at once.
I’m able to test:
Signal strength in the area
433 modules I want to use
Antennas I want to use
The transmission logic I want to use
Different ASK protocols
All this with a wireless, rechargeable and easily customizable package. At the moment this is not a commercial product however I have many other devices that work with the Roboguard ecosystem that have commercial applications.
Back view of the PCB. This was made around the ATtiny212 MCU and the SYN1115 transmitter.
A few years ago I wanted to use some type of sensor for security purposes in my workshop. I just needed something to sense movement and send a radio signal to my Roboguard device. An actual Roboguard beam was too expensive, too bulky and large and was not rechargeable… not to mention a bit overkill for my application.
So I decided to look for a low power and small sized PIR sensor. Eventually I was able to find an affordable and small PIR sensor that can operate at 3.3V. I found the MH-SR602 PIR sensor which offers an adjustable delay time with a detection distance of 0 – 3.5 Metres. it has a built in regulator with a range of 3.3 – 15VDC but adds a bit of extra current draw… since I was already using 3.3V for my IC and RF circuits I was able to de-solder the included regulator to save a bit of current. This would help me greatly especially since I was going to use deep sleep.
PCB inside the box I designed it for.
Lid closed only the PIR sensor is sticking out (Radar does not have this problem)
Now the main MCU is the ATTiny212 and the RF module used is the WL102-341… not sure on the authenticity of the module but it works range is good and the current draw is up to spec + the EN pin does disable the unnecessary current draw when pulled low. The LDO regulator I used is the classic HT7333-A.
After soldering everything and checking for shorts I was able to program the MCU and then power up the device with an recycled 550mAh vape battery. First thing I noticed the device would constantly trigger the PIR. Eventually after a long time of troubleshooting I replaced one of the ceramic capacitors used to stabilize the output of the HT7333-A and now everything worked… Now when looking at the capacitor I didn’t understand exactly why it was not working, there was no short only a really high resistance and the capacity was a bit higher than the specified uf.
Before hand I made sure the PCB would fit into a standard rectangular project box. I just needed to drill a hole for the PIR sensor to stick out. After drilling a hole for the micro USB charging port the project was complete and working.
While testing I was able to achieve a very low current draw in deep sleep mode. I did some basic calculations and the MCU should last more then a year without needing a charge. Later after leaving the device in my workshop I was able to confirm this with the device lasting over a year and a half with mild triggering whenever I was working in the workshop. making use of the ATtiny PIT for long sleep timing and interrupts for waking up the device after some code refactoring I was able to make things super efficient. I programmed everything in C. ASMM is a bit to much for low level stuff in my opinion though I would like to make time to learn it one day. Still I was able to create a program of 956 bytes using ram of 18 bytes. So under 1k was nice since the smallest ATtiny size is 2k so I’ve still got plenty of space.
Current when the MCU is in sleep mode (the PIR is always running) 121.9uA roundabouts
772.2uA of current when the MCU is running but RF is not TX’ing
13.1mA during TX
One thing I can say for sure is that this project really activated a habit in me to try make everything as small and as efficient as possible whenever I program 8-bit microcontrollers for my personal projects. I must say I was also able to save some money when buying IC’s by improving my code and what can I say it feels very good once a project is completed and as small and efficient as I could make it.
With that being said sometimes when using a microcontroller like the ESP8266 or ESP32 the resource abundance feels crazy but once I start populating all that space with HTML and bitmaps + other media I quickly realized that even that space can get used up very fast.
