This isn’t completed but the general shape and assembly for the Cat Feeder Unreminder is going to look like this. A 3D printed enclosure with a grove in it that the solar panel slides into. Then the PCB fastens to the front which captives the solar panel. Then on the PCB there will be soldered threaded inserts where a plexi front panel will fasten to.
I got the entire project onto a breadboard… mostly! A combination of evaluation boards and breakout boards and I was able to verify all the subsystems are working correctly together.
The entire system draws ~5.6uA at 3.3V from the super capacitors. Measured through the uCurrent.
Here is the breadboard with the subsystems called out.
Up next is to complete the enclosure design and then the board layout!
This is the display I am using for the Cat Feeder Unreminder. Part Number: VI-422-DP-RC-S
The display is a Twisted Nematic (TN) style LCD for low power. I talked about this display in a previous post.
You can find the footprint in my eagle parts library in displays.
Here is the current schematic for the Cat Feeder Unreminder! Just need to wire up the display.
Based on my testing of the evaluation board, this is the schematic for the LTC2956 I am using in the Cat Feeder Unreminder.
The resistor from RANGE to LONG pin is set to 100K ohms. This is specified in the datasheet.
To set the actual time for the timer to activate the EN pin (t PERIOD), You need to first select the range resistance from the chart below. In my case I want to activate every 22hrs. 162K ohms is the resistor I chose which sets NRANGE to 262,144.
To calculate the period resistor, this is the formula provided by in the datasheet.
RPERIOD = 400 • tPERIOD/NRANGE
For 22hrs, tPERIOD becomes 22 x 60 x 60 x 1000 = 79,200,000. This gives an R PERIOD of 120,849.609 ohms. I picked a 121K ohm resistor.
To send the device into the sleep state, I tied the SLEEP signal through a switch to VCC (3.3V). This brings SLEEP high on button press. When the button is released, SLEEP has a falling edge which is what the LTC2956 is looking for to send it into the sleep state.
In trying to reduce the power consumption of the Cat Feeder Unreminder, I am going to explore using some really low power comparators to build the AC drive voltage I need to run the TN LCD segments.
The MAX9019 is a dual package comparator fits the bill in the power requirements.
In the switching frequencies I am using (50-100Hz) it should only need a supply current of ~1uA.
We setup the first comparator to generate a square wave and then the second comparator in the package as an inverter.
The design breadboarded up. It drives the screen!
This is well under the resolution of my Siglent SDM3045X. Will have to wait to get the right equipment to measure the actual current the circuit is drawing.
Here are the two output drive signals on the scope.
Next step to work on is the power retention system. The largest draw on the system right now is the leakage on the super capacitors! I found some super capacitors made by Eaton, HSL0814-3R8106-R, that specialize in having low leakage. Slightly higher ESR then some super capacitors but that isn’t that important for this project.
At MacroFab we have a large industrial air compressor that provides compressed air to our pick and place and various machines. I want to monitor the compressors pressure and run time to help influence the maintenance schedule for it.
Compressor IoT part list
- IMU for vibration sensing
- iNEMO inertial module: 3D accelerometer, 3D gyroscope, 3D magnetometer
- 3.3V, I2C
- MEMS Microphone
- Analog signal, will be boosted with an opamp
- Board Mount Temperature Sensors Low Power Digital Temp Sensor
- 3.3V, I2C
- Ebay Pressure Transducer
- 1/8″ NPT Male fitting
- Analog output 0.5V – 4.5V over pressure range
- SSR to control the compressor switch
- 3VDC to 32VDC control signal
- Place 10ohm in series from pin from particle photon for protection.
- TVS 3.3V for transient protection.
- Enclosure with flange
- Particle Photon
- IoT platform
You can find the files on my github.
Working on this fan controller for my Jeep. All the files are on github. Uses a 4×40 character VFD. Has an onboard E-compass module that will show inclination and direction. Part number is FXOS8700CQR1.
I am still working on the Gameboy VGA driver. You can see the code and hardware working on the BenHeck Show. I have to get some other projects done before I can finish the Gameboy :)
Parts, PCBs, and Stencils arrived earlier this week so I put together the three prototypes for REV4. Above is pre reflow.
Directly after reflow.
Magnified picture of the board. Turned out great. FTDI chip flashes and Propeller programs over USB. The new MAX11613 ADC works as well. I will be posting the driver code for that shortly.
Some changes from REV 3 to REV 4.
Render of the PCB from OSHPark.
Top stencil pattern. The through hole pads on the micro USB connector are going to be soldered with the “Paste In Hole” method. I have not tried this yet but if it works I will be able to cut out an entire operation during production of the boards.