Peta-pico-Voltron is an easy-to-build, affordable power supply. One of its limitations is that it requires a computer to run the user interface, and an external power supply. The Python interface can run on a multitude of platforms and allows to mitigate the first issue by allowing to run the interface on tablets, but the requirement for a power supply still remains.
Here we present a completely standalone version of the Peta-pico-voltron power supply, which includes a rechargeable Li-po battery, and a touchscreen.
The bill of materials for the stand-alone configuration is available on the download page. One sheet of the excel file describes the component required for the battery management circuit, and the other sheet describes the other components required (battery, Raspberry Pi, touchscreen, etc.)
Required components and preparation
High Voltage power supply
- You need a fully functional single channel high voltage power supply. Follow the instructions on this web site to assemble, configure, and calibrate a single channel HVPS.
- In the assembly procedure, be sure to solder the 2-pin headers hD3 and hS2, as the main switch and the HV on LED will be panel mounted.
- Once your HVPS is assembled and calibrated, connect it to a computer (see Direct communication with the HVPS) and enter the command SPowJack 0 to tell the HVPS that the external power doesn’t come from the DC jack J1.
- On the HVPS PCB, move the jumper h5V from the on to the off position. The HVPS won’t be powered by the DC jack, but directly by the 5V line on the 10-pin header.
Raspberry Pi and LCD touch screen
- You will need a Raspberry Pi (Raspberry Pi 3 Model B, 16GB Micro SD Card with NOOBS Pre-loaded)
- You will also need the 7” LCD touchscreen (Raspberry Pi 7″ Touch Screen Display with 10 Finger Capacitive Touch)
- Connect the Raspberry Pi to a monitor (this doesn’t need to be the LCD touchscreen at this stage. You can use the HDMI connector of the Pi to connect to any monitor).
- Install the python graphic user interface. In preparation of the use of the interface on the touch screen, and because the interface uses the entire screen, it is recommended to auto-hide the taskbar of the Raspberry Pi. To auto-hide the task-bar, right-click on it and select ‘‘Panel Settings”. Click on the ‘‘Advanced” tab, and check ‘‘Minimize panel when not in use”.
- If you intend to use the USB port of the battery management circuit to send commands to the HVPS (to be able to control the HVPS with an external computer), follow the instructions described in the file install.txt located in the Python interface folder.
- Connect the HVPS to one of the Raspberry Pi USB ports, and check that the interface and the HVPS are communicating.
Pre-assembly of touch screen and Raspberry Pi
- On the LCD touchscreen control board, install the flat cable on the right and install a power cable on the 5pin GPIO connector of the controller. You can solder the cable directly to the GPIO GND and 5V pins. At the other end, install the connector P10 mate (Digikey WM2014-ND, 5 Position Rectangular Housing Connector Receptacle White)
- Install the Raspberry Pi on top of the touchscreen control circuit, as illustrated in the figure below. Use the M2.5 screws included with the screen to secure the Pi, except on the top left corner, where you should use the M2.5 30mm spacer (Digikey AE10789-ND, HEX STANDOFF M2.5 BRASS 30MM). Connect the display cable to the Raspberry Pi
Battery Management circuit
The Battery management circuit functionalities are described on the battery management PCB page.
The sheet Battery Management PCB of the stand-alone configuration BOM lists all the components required to assemble the battery management PCB, and the Altium/Gerber PCB files are available in the download section. The silk overlay on the PCB gives all the indication required on the location of each component, and assembling the board should therefore be straightforward.
- Solder the components of the bill of materials of the battery management PCB (sheet Battery management PCB) on the board. The names of the components are clearly labelled on the PCB silkscreen and correspond to the name given in the bill of material (column Designator).
- Prepare the LEDs (2 (recommend red and green) for the battery management circuit, 1 for the HVPS high voltage on indicator), Switches (1 for power, 1 for high voltage enable on the HVPS), thermistors, and battery with wires and the appropriate connector (see bill of materials). The figure below illustrates the different connectors on the battery management PCB (but P7, P8, P13, and P14) have been replaced by 2-pin headers).
Housing for the stand-alone configuration
You will find a zip archive in the download page, enclosure section with a Solidworks model of an enclosure for the stand-alone configuration. There is a Laser_cutting subfolder with SVG files ready to be cut with a laser cutter. Each part should be cut in a 3 mm plastic sheet (e.g. PMMA), except for HVPS_support.svg that needs to be cut in a 6mm plate. This part also requires the addition of two M2 tapped holes on the side, as shown on the Solidwork file of this part (enclosure/HVPS_support.SLDPRT) that are used to hold the HVPS PCB. Double-sided adhesive can also be used instead, if you want to avoid adding the two M2 holes. The file complete_assembly.SLDASM shows how all parts fit together. Glue is required to assemble the different parts. Use a glue compatible with the plastic you are using.
Pre-assembly of the enclosure
- Cut all parts of the file screen_holder.svg in a 3mm-thick plastic plate, such as PMMA. The text indications included on the part can either be etched on the surface, or should be written with a pen, as they help placing the parts for which orientation matter.
- In the above file, the 4 identical parts are used to hold together the top and bottom plates to the sides. The two 2.5 mm holes in each part must be threaded with a M3 tap.
- Cut the part HVPS_support.svg in a 6mm-thick plastic plate. This part also requires the addition of two M2 tapped holes on the side, as shown on the Solidwork file of this part (enclosure/HVPS_support.SLDPRT) that are used to hold the HVPS PCB. Double-sided adhesive can also be used instead, if you want to avoid adding the two M2 holes.
- Assemble all of the parts you have prepared according to the image below. Pay attention to the orientation of the different parts. You should be able to clear any ambiguity by referring to the picture. (Note the two M2 screws that have been added to indicate the location of the two M2 holes on the part HVPS_support). Use glue to hold the parts together. You will have two parts left that will be used for the bottom of the box.
- Cut the parts side_1.svg, side_2.svg, side_3.svg, and side_4.svg and assemble them as shown on the image below. The text added to the SVG file indicate which side of the parts goes in the inside of the enclosure. In addition, the text should be oriented in the same direction on the four different parts.
- Cut the part bottom.svg and assemble the two parts that remain from the screen holder in the holes on the side
- Install the two switches and the 3 LEDs on the side of the enclosure. Use a bit of glue to hold the LEDs.
- Use double-sided tape to attach the battery (AliExpress 32612003056, 3.7 V 10000 mah tablet battery brand tablet gm lithium polymer battery) to the bottom plate. Fix the two thermistors with tape at different location on the battery. It is also recommended to add an insulation layer on top of the battery, such as a thin PET sheet, or some polyimide tape to protect is from the high voltage of the HVPS PCB.
Assembly of the stand-alone unit
- Insert the LCD screen with the Pi in the screen holder. On the left, use two M3 screws to secure the screen to the holder to the screen. On the right place the Management PCB first on top of the screen holder, and use two M3 screws to hold together the PCB, the screen holder and the screen (see picture, but note that the wires on the top of the battery management PCB have been replaced by headers)
- Use a flat cable (20 lines) to connect connector P2 on the batter management PCB to pins 1 to 20 of the Raspberry Pi GPIO port. Ifyou use a 20-pin connector on the Raspberry Pi side, you will need to cut pins 21 and 22 of the GPIO port. You can also use a 40-pin connector and clamp the 20-wire cable on pins 1–20. The power connector of the screen is connected to P10 on the battery management PCB.
- Install the HVPS PCB on top, fixing it on the 30 mm post with a M2.5 screw, and on the HVPS_holder part on the left with 2 M2 screws, or with adhesive if you haven’t made holes for the screws.
- Prepare a cable to power the HVPS with 2 5-pin connectors (Digikey WM2014-ND, 5 Position Rectangular Housing Connector Receptacle White). 5 V is on pin 2, and GND on pin 4. One end connects to connector P11 of the battery management PCB, and the other end to pins 1-5 of the 10-pin header of the HVPS.
- Use the right angle USB cable (Aliexpress 32753222490, Right Angle Micro USB Data Cable 5 Pin Micro Male to 2.0 A Male Data Sync Charger Cable Converter 90 Degree Adapter SP Right 1PC) to connect the HVPS to one of the USB ports of the Raspberry Pi.
- Add the enclosure side and use 4 M3 screws to secure it to the front panel
- Connects of the components to the battery management PCB (some of the connections have already been described but are repeated here):
- P1: Place a jumper on P1 to enable charging via the USB port
- P2 brings power and logic signals to the Raspberry Pi. Use a flat cable to connect to pins 1 to 20 of the Raspberry Pi. If you use a 20-pin connector on the Raspberry Pi side, you will need to cut pins 21 and 22 of the GPIO port. You can also use a 40-pin connector and clamp the 20-wire cable on pins 1–20.
- P6 is the battery connector. To handle the high current, two wires should be connected in parallel. Pins 1 and 2 connect to the positive pole of the battery and pins 3 and 4 to the negative pole. P6 is polarised and prevents plugging the battery in the wrong way. Take care to solder P6 with an orientation matching the battery plug.
- P7 and P8 connect to 10 kΩ NTC thermistors that must be applied on the battery to monitor its temperature
- P9 is the connector for the main power switch and connects to switch 1 (image above) . To handle the large current, two wires are used for each contact, with pins 1 and 2 sending VSYS to the switch, and pins 3 and 4 receiving the return signal (c.f. Boost converter section of the battery management PCB page).
- P10 powers the LCD screen controller. 5 V is on pin 1, and GND on pin 5. It connects to connector J1 on the screenc ontroller.
- P11 powers the HVPS. 5 V is on pin 2, and GND on pin 4. 5 V connects to pins 2 and GND connects to pin 4 of the 10-pinheader on the HVPS PCB.
- P13 connects to the status LED (marked 3 in image above). It is on when the battery is charging
- P14 connects to the power good LED (marked 2 image above). It is on when the unit is connected to a source of power.
- Connect the component to the HVPS
- The right angle USB cable connects the HVPS to the Raspberry Pi
- Button 4 is the high voltage safety switch which connects to header S2 on the HVPS PCB
- LED 5 (red) indicates the presence of HV on the output, and is connected to hD3 on the HVPS PCB.
- Once everything is connected, place the bottom cover with the battery on top of the assembly, taking care that the wires are all inside the enclosure and located on the battery management side of the box (i.e. away from the high voltage side of the HVPS), and fix the bottom to the side using 4 M3 screws.
Usage of the stand-alone configuration
- Check that the safety switch (Switch 4 on figure above) is in the ‘0’ position to disable the high voltage circuit.
- Place main switch (Switch 1 on figure above) in position ‘1’ and wait until the Raspberry Pi has started.
- Start the Python interface (file install.txt in the interface main folder) has instructions to place a shortcut on the desktop, or to have the interface launched automatically on start up. The section on the Python user interface has detailed instructions on the use of the interface.
- Once you have exited the interface, you are back on the Rasbian desktop
- Don’t forget to put the HV safety switch on ‘0’ if not done already for additional safety.
- Use the desktop startup menu to shutdown the Pi
- Caution: As soon as you press the sutdown button, the LCD screen goes black. However, it takes about about 30 second for the Pi to turn off. Wait 1 minute. If you don’t do it and you switch off power too early, this can lead to corruption of files or of the SD card
- Turn off main power switch (switch 1 on figure above). Note that there is no light indicator change for this operation, so do not forget to turn off the main power, or the LCD and Pi will still be powered, which will drain the battery
A note on the battery
There is unfortunately no indication of the charge level of the battery at the moment. If you use the stand-alone HVPS for too long without connection to a power supply, it will turn off without warning you.
In case of trouble
In case of trouble with the Pi, or to update the interface or the OS, you can open the case and remove the side. It will then be possible to access the RJ45 Network plug and USB connector of the PI to connect a mouse and keyboard, and to connect your Pi to the newtwork, without disassembling everything. You can also remote access the Pi via Wifi with VNC.