Category Archives: Projects

MAX6682 Breakout Board and Reading Thermistors

To read oil and coolant temperature on the Jeep I wanted to use automotive parts for the sensors. Most temperature sensors in the automotive world are thermistors. I searched around for some in 1/8″ NPT and found some designed for aftermarket gauges. Only problem was there was no datasheet for them…which is necessary to accurately read the thermistors since they are non linear devices. At under $4 a piece I ordered them  anyways.

Thermistors with part number MX61573 and YC100665.
Thermistors with part number MX61573 and YC100665.


Fortunately when they arrived they had a part number on them and after some googling I managed to find a temperature chart.

Temperature to resistance chart for the MX61573 Thermistors
Temperature to resistance chart for the MX61573 Thermistors.


I double checked the values with a multimeter and setting the hot air gun to the temperatures in the chart above and seeing what the resistance was. Everything matched.

To read the thermistors I decided to use the MAX6682 IC. This IC gets rid of power supply noise and thermal self heating of the thermistor.

The only thing I had to calculate was the REXT value. I used the 2031 ohm (20C) for RMAX, 108 ohm (100C) for RMIN, and 388 ohm (60C) for RMID. This came out to a value of 287 ohms.  Which the resistor ERA-3AEB2870V by Panasonic works. See page 6 of the datesheet for the formula to calculate REXT.

Then I drew up the schematic and layout for the breakout board.

Schematic for the MAX6682 Breakout Board.
Schematic for the MAX6682 Breakout Board.
Layout for the MAX6682 Breakout Board.
Layout for the MAX6682 Breakout Board.


I added a little header (J3) that will allow me to easily change the REXT value for other thermistors.

MacroFab PCB Render.
MacroFab PCB Render.


Boards ordered!


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.

DGN and Gameboy Update

This is something I recorded with Stephen Kraig (Co-host of the MacroFab Engineering Podcast) back in September 2016. We never made it public till now! Drunken Gaming Night! It is silly and I have no idea where Stephen and I will take the channel but it is fun to do.

Things to finish on the Gameboy VGA Design

  • Pick a VGA connector
  • 3.3V TTL -> Analog VGA signal
    • Resistor ladder seems to be the best way to do this
    • Current development board uses 4bit VGA with 500Ω, 1kΩ, 2kΩ, and 4kΩ resistors
  • Serial Terminal
    • FT230X -> USB
  • Designing a flat flex cable
    • Solder one end to the FPGA PCB
    • One end fits into the FCC connector on the Gameboy

DMG VGA Mod Voltage Level Shifter Section

The DMG-01 Gameboy runs off all 5V logic and the FPGA I will be using (Cyclone 4 Altera) runs off 3.3V I/O. Conversion is needed to prevent frying the FPGA. I have used the TI part SN74LVC8T245 in the past with other FPGA projects and on the proof of concept VGA mod with the DE0 dev board.

The SN74LVC8T245’s output enable is active low so I pulled it high with a 10K resistor. This way the convertor is disabled till the FPGA can control the IC. Direction is set by default to be 5V -> 3.3V conversion with a 10K pull down.

I am also going to pull in the state of the buttons on the Gameboy. I hope to be able to have different modes that the FPGA can perform. Resolution changes and the like. Eventually I will design it so that FPGA can also drive the screen but that will probably be a future hardware revision.

Oh boy, here we go posting again

Instead of trying to have an excuse of why I have not been posting here. Well go check out MacroFab. It is the company I co-founded a bit over 4 years ago now. I also am the co-host of the MEP or MacroFab Engineering Podcast. It is a weekly electronics podcast and we are currently on episode 119…and we have not missed a single week!

I have been doing side projects for fun but I have just been very bad about posting them here. Typically they just go to my twitter account and I talk about them on the podcast. I will be putting more effort into posting here.

With that out of the way… Current plan is to just look at my past incomplete projects and either finish them or kill them off. Starting with the FPGA Gameboy project. First order of business is to start making some dedicated hardware for the Gameboy. To quicken the development process I am going to lift the FPGA design block from the ChromaColor project. The FPGA is an older Cyclone 4 module (EP4CE6E22C8N) but it should do the trick and is still fairly affordable. I would like to move it to a newer platform like a 10M08SCU169C8G.

Spooky Sound System PT. 2

Routing the audio amp. Since this is going to be made in 500+ QTY of units I decided 4 layer was the way to go as the budget allowed for it. For the layers I will be using the top and bottom side as signals and the two inner planes as the GND and “virtual” GND of the system. Power will be on the bottom layer. Everything is pretty much routed but I need to clean up the traces now.


Spooky Sound System

I have been working on this amplifier for pinball machines. It is a simple 2.1 system with volume control, tone control, sub cutoff, and sub volume. The main lifting is done by a 4 channel TDA7387 which is mainly for low cost car stereos. It can do 41W so it should be plenty powerful for a pinball machine. For opamps I am using the AZ4558C. This is a generic audio opamp in a dual package.

It is a single supply design so easy integration and makes it able to use low cost switcher style power supplies. I run the power though an opamp set to half gain to create a “virtual ground”. This is the middle bias point for all the filtering. After filtering it then gets DC blocked with in series capacitors and shoved into the TDA7387.


After I route this and organize the schematic I will post a link to the files.

Prop based Fan Controller for Jeep


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 :)