Category Archives: Projects

Cat Feeder Unreminder Breadboarded

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!

LTC2956 Schematic for the Cat Feeder Unreminder

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.


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.

More Oscillators but with Comparators

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.

Compressor IoT 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.

Stephen and I talked about the Compressor IoT project on the following Podcasts: MEP EP#68, MEP EP#70, and MEP EP#74.

Compressor IoT part list

  • LSM9DS1
    • IMU for vibration sensing
    • iNEMO inertial module: 3D accelerometer, 3D gyroscope, 3D magnetometer
    • 3.3V, I2C
  • SPU0410HR5H-PB
    • MEMS Microphone
    • 3.3V
    • Analog signal, will be boosted with an opamp
  • TMP102
    • Board Mount Temperature Sensors Low Power Digital Temp Sensor
    • 3.3V, I2C
  • Ebay Pressure Transducer
    • 1/8″ NPT Male fitting
    • 5.0V
    • Analog output 0.5V – 4.5V over pressure range
  • 6225AXXSZS-DC3
    • 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.
  • 1591XXSFLBK
    • Enclosure with flange
  • Particle Photon
    • IoT platform

Compressor IoT Schematic


Compressor IoT Layout

You  can find the files on my github.

Prop Dev Stick REV4 Update


Some changes from REV 3 to REV 4.

  • Micro SD Card Slot changed. Old one was Molex MFG# 502570-0893. New part is 4UCON MFG# 15882.
  • Tact Switch changed to more low profile switch.
  • ADC switched from AD7999YRJZ-1500RL7 to MAX11613EUA+. Slower ADC but increase from 8bit to 12bit resolution.
  • Changed Voltage Regulator from TS2937CW33 to NCP1117LPST33T3G.
  • Added 10uF Electrolytic Cap to 3.3V rail.
  • Crystal changed to low profile ABMM-6.000MHZ-B2-T.
  • Added voltage divider to switch to USB power if external power falls near cutoff for regulator.

    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.