The new firmware has the following enhancements.
- Dynamically controlled boost pulse widths to allow the the boost voltages to be set more accurately at lower voltages. The original utracer firmware used only 5us and 20us widths.
- All measurements are over-sampled to lower noise and improve accuracy.
- The heater voltage accuracy* is improved by changing the PWM frequency to 2KHz.
- Grid voltage 12bit resolution (4096 steps) upgrade from original 10 bit (1024 steps)
- Calibration data saved to chip for portability
- V3 introduces firmware that can be updated from the uTmax GUI
- Fast data capture reduces the voltage drop during sampling to just 0.8V at 400mA. The stock firmware is approx 2V.
- V3.07 introduces a switchable low current range for greater accuracy. More about this under “Switchable Current Ranges” below
*To make the most of the lower heater frequency, you should short out inductor L2 in the heater supply of your uTracer. This will demand high peak currents from the power supply which could cause an issue if the one you are using is not rated for sufficient current. If you find that is a problem you will need to replace the 0.4A 330uH and 0.5 ohm inductor with something more suitable. Something around 680uH 0.1 ohm (or lower) and at least 1.5A. You should also change C6 to 4700uF.
Recent testing suggests the circuit impedance for the heater is around 0.12 ohms at 6.3V. This is is large part likely to be due to the Rds(on) of the FET used in the heater circuit. You should allow for this voltage drop when choosing the heater voltage i.e add 0.12V to the specified heater voltage for each amp of heater current.
12 bit grid voltage requires the latest uTmax. The uTracer GUI is 10 bit only.
To install you simply swap the new chip for the old one. Edit the “Firmware=100” line in the cal.txt file to read “Firmware=200”. Now run the GUI and use the speedy calibration wizard. That’s it!
From GUI V3.05, the firmware can be updated from the uTmax GUI “Utilities” menu. You can download them here.
- V3.03 Adds -100V grid voltage with additional hardware. Please look at the “-100V” section for a schematic. This is essentially the same as Ronald’s but with some typos fixed.
- V3.04 Has improvements to the speed
- V3.05 Ensures all boost pulses are off before starting an update
- V3.06 Fixes random incorrect samples
- V3.07 Current range switch for better accuracy
There is an issue with the OPA227 chips while updating the firmware. The problem is the negative supply is turned off during updates and any glitch on pin 3 will cause them to latch up and overheat. You can unplug the chips before updating or better, add a 4.99K resistor in series with pin 3 and never have to worry about it again.
After the upgrade go to calibration and hit “save” to save the previous calibration to the chip.