For keeping the time for the Cat Feeder Unreminder I am planning on using the LTC2956-1 which is a super low power timer that has push button reset control. It can accurately handle very long timers that a traditional RC style timers (think 555 timer) wouldn’t be able to do.
Received the 3AAEM10941CPCX10 evaluation kit for the AEM10941 solar harvesting chip today.
Its possible it won’t light up right away. It takes sometime for the super capacitor to charge up. You can charge up the super capacitor with a power supply set to 3.3V and current limited to around 10-20mA. Make sure to not reverse bias the charging!
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.
Fortunately when they arrived they had a part number on them and after some googling I managed to find a temperature chart.
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.
I added a little header (J3) that will allow me to easily change the REXT value for other thermistors.
Design ended up having only 10 LVDS signals broken out as that required less unique parts. The connectors are expensive (1-282834-0) running ~$5.70 in singles. I will be looking into alternatives to see if I can get the cost down. I found some on AliExpress but I will need to order them and test them to see if they are any good.
I also included a 4 position auxiliary power connector to power up external circuits. No power safety though (fuses/TVS) so use at your own risk!
Started work on a expansion board for the DE0 FPGA development board. Planning on having 4 8-bit bi-directional level shifters giving 32 I/O and breaking out 12 LVDS signals to screw terminals. Basically a simple digital acquisition add on. Using the expansion template I made for the DE0 a couple days ago.
LVDS will be buffered to protect the FPGA. Have not picked the buffer chip yet. The bi-directional level shifter is the SN74LVC8T245PWR by Ti. Handles 1.65V to 5.5V on both sides and has basic ESD protection. I am debating putting over voltage protection on the I/O of the level shifters. A 50ohm resistor in series with the I/O plus a 5.6V TVS Diode should do the trick and not add to much cost to the board.
Here is the Booster Pack built. Tested and it works! I will be posting the code tomorrow after I clean it up some. Includes PWM for both channels and encoders (untested however). I will release a version with and without the encoders.