Nestronics
Nestronics
NOTE: WORK IN PROGRESS FOR DOCUMENTING THE UREBS-07 CONTROLLER. This new version uses PSPWM (Phase Shift Pulse Width Modulation) to control the field strenght level.
Index
Controller Details
Schematic
C++ Firmware plus web page PHP
Gerber Files
The MCU generates a clock signal at twice the desired resonant frequency using the internal hardware timers. Each resonant circuit uses a full bridge driver
which requires 2 lines to drive it. We will call these the A and B legs. The A and B legs are both 50% duty cycle signals at the resonant frequency.
When the A and B legs are 180 degs out of phase the full bridge driver, drives the resonance at maximun power capability.
The other extreme is when A and Be are in phase, which results in no power delivered to from the full bridge driver.
Phase shifts varying from 0 to 180 degs will give a varying amount of power.
Hence the name Phase Shift Modulation. When we have a control signal at twice the frequency of resonance, and we toggle the A leg on every
rising edge, and the B leg on every falling edge we acheive:
1. both A and B legs will always be 50% duty cycle (desireable)
2. Duty Cycle control on the the orginal X2 resonant frequency signal controls the phase shift between the A and B legs, and hence controls
the output power delivered from the full bridge driver.
Note that this method allows for power adjust for each cycle of the output. This is highly desireable as all resonance takes time to build up
to maximun power, and by providing a boost in power to start the resonance reduces the time required to get to the desired output field strenght.
The boost allows a faster rise time during the start of the resonant burst.
Individual Zero crossing detectors, and peak detectors allow feedback to the MCU of the peak resonant voltage and phase of each coil pair.
Since the exact phase at resonant can vary in accuracy, the MCU is capable of adjusting the phase relationship (in a feedback loop)
to ensure the resulting produced phase difference is 90 degs. However the current version of software has an calibration routine for
calibrating levels and phase, and saving them. The UREBS then just uses these values, so the feedback loop is not always active (only during calibration).
A Raspberry Pi 5 is used for a Web Server which is accessible over the WiFi built into the Raspberry Pi. Web Page access
(from any phone or tablet, etc) is used to control the setting on the UREBS controller.
Shown below is revision 7 of the PCB which has phase shift control of the A and B legs to allow a high or low drive level.
(Note that Revision 7 uses up to a 55V supply)
Note how 20ga bus wire is used to re-enforce the current handling capability of the PCB. The peak current to start the burst
could be greater than 100A as the multiple 22,000ufd caps discharge.
A Capacitor bank is used for each of the two resonate circuits. The resonate frequency is manually tuned for 265Hz (or desired freq) by increasing/decreasing
capacitance for the peak resonance voltage. The 2nd resonance(the one lagging 90 degrees) is also tuned to ensure and approximate 90 phase shift.
The MCU will autotune the phase once the initial manually tuning is down. Ideally 90 degrees matches a duty cycle of 50%. The MCU changes the duty cycle
to fine tune the phase.
The Capacitors should be rated for pulse use and have a high RMS voltage rating. Here the capacitors are the Kemet R75 series with a RMS voltage rating of 600V.
Great caution should be used when working with the high voltage produce by this circuit. Use all caution to prevent electrical shock/death.
Note the Schematic has different pages selected by the tabs. Also the schematic is not yet fully completed but the basics are there.
Link to the SchemeIt schematic and bill of material for the UREBS01
Detailed Component Selection
Firmware for the MCU
The main MicroController is a Texas Instruments MSP430FR5739IRHAT that has 16KB of FRAM.
It can be programmed using the CCS (Code Composer Studio) that is free from TI.
You can program it with an Experimenters board
or a Flash Emulation Tool.
In both cases you need to build a custom 2 wire (4 wires with power and ground) programming cable.
main MCU1 firmware download link
There is also a 2nd MCU, the MSP430FR2433, used to monitor levels. It can be programmed with the same programmer and cable.
firmware download link
The Raspberry Pi must have the apache/php web server software install, as well as cpp.
The c plus plus program interfaces with the I2C interface to the UREBS. Then the web server, serves that information so
that the UREBS can be controlled from a simple web page.
download cpp firmware
download web page
Gerber files for the Printed Circuit Board (PCB)
UREBS revision 7 gerber files download link
This version of PCB (printed circuit board) has removed some artwork errors, but has not been tested yet.
Note please review the readme file for instruction on order parameters.
You would also want to order a solder screen, to allow assembly of the board.
All our PCB's are build by hand, using air tool placement, and reflowed in a low cost portable reflow oven.
Thru hole components are then installed.
A part placement guide can be downloaded here .
We commonly print out a few copies and use different colors of highlighters to mark same value of components.
This greatly speeds the placement rate.