Here’s another active balancing circuit for large ultracapacitor banks, this one is designed for a series string of 6, at 2.5v per capacitor.
Based on the design here, I have transcribed the circuit into Eagle & designed a PCB layout.
As can be seen from the circuit diagram above, this is just 6 copies of the circuit from the above link, with screw terminals to attach to the capacitor string.
And here’s the PCB. the MOSFETs & OpAmps are very small SMT parts, so require a steady hand in soldering. This board can easily be etched by hand as there’s only 3 links on the top side. No need for a double sided PCB.
As always, the Eagle project files & my Eagle library collection are available below:OpAmp Ultracapacitor Balancer (70) Eagle Libraries (75)
Continuing from my previous post where I published an Eagle design layout for AD7C‘s Arduino powered VFO, here is a completed board.
I have made some alterations to the design since posting, which are reflected in the artwork download in that post, mainly due to Eagle having a slight psychotic episode making me ground one of the display control signals!
The amplifier section is unpopulated & bypassed as I was getting some bad distortion effects from that section, some more work is needed there.
The Arduino Pro Mini is situated under the display, and the 5v rail is provided by the LM7805 on the lower left corner.
Current draw at 12v input is 150mA, for a power of 1.8W total. About 1W of this is dissipated in the LM7805 regulator, so I have also done a layout with an LM2574 Switching Regulator.
The SMPS version should draw a lot let power, as less is being dissipated in the power supply, but this version is more complex.
Here the SMPS circuit can be seen on the left hand side of the board, completely replacing the linear regulator.
I have not yet built this design, so I don’t know what kind of effect this will have on the output signal, versus the linear regulator. I have a feeling that the switching frequency of the LM2574 (52kHz) might produce some interference on the output of the DDS module. However I have designed this section to the standards in the datasheet, so this should be minimal.
Nevertheless this version is included in the Downloads section at the bottom of this post.
The output coupled through a 100nF capacitor is very clean, as can be seen below, outputting a 1kHz signal. Oscilloscope scale is 0.5ms/div & 1V/div.
Thanks again to Rich over at AD7C for the very useful tool design!
Linked below is the Eagle design files for this project, along with my libraries used to create it.AD9850 DDS VFO Eagle Files (350) Eagle Libraries (75) AD9850 DDS VFO SMPS Version (169)
OK, a few revisions have been made to the water management PCB, mainly to reduce the possibility of the brushed DC motors in the water pumps from causing the MCU to crash, with the other changes to the I/O connector positioning & finally upgrading the reverse blocking diode to a 10A capable version rather than 5A.
Having two separate water tanks on nb Tanya Louise, with individual pumps, meant that monitoring water levels in tanks & keeping them topped up without emptying & having to reprime pumps every time was a hassle.
To this end I have designed & built this device, to monitor water usage from the individual tanks & automatically switch over when the tank in use nears empty, alerting the user in the process so the empty tanks can be refilled.
Based around an ATMega328, the unit reads a pair of sensors, fitted into the suction line of each pump from the tanks. The calculated flow is displayed on the 20×4 LCD, & logged to EEPROM, in case of power failure.
When the tank in use reaches a preset number of litres flowed, (currently hardcoded, but user input will be implemented soon), the pump is disabled & the other tank pump is enabled. This is also indicated on the display by the arrow to the left of the flow register. Tank switching is alerted by the built in beeper.
It is also possible to manually select a tank to use, & disable automatic operation.
Resetting the individual tank registers is done by a pair of pushbuttons, the total flow register is non-resettable, unless a hard reset is performed to clear the onboard EEPROM.
View of the main PCB is above, with the central Arduino Pro Mini module hosting the backend code. 12-24v power input, sensor input & 5v sensor power output is on the connectors on the left, while the pair of pump outputs is on the bottom right, switched by a pair of IRFZ44N logic-level MOSFETS. Onboard 5v power for the logic is provided by the LM7805 top right.
Code & PCB design is still under development, but I will most likely post the design files & Arduino sketch once some more polishing has been done.
Here is a simple 555 timer based flyback transformer driver, with the PCB designed by myself for some HV experiments. Above is the Eagle CAD board layout.
The 555 timer is in astable mode, generating a frequency from about 22kHz to 55kHz, depending on the position of the potentiometer. The variable frequency is to allow the circuit to be tuned to the resonant frequency of the flyback transformer in use.
This is switched through a pair of buffer transistors into a large STW45NM60 MOSFET, rated at 650v 45A.
Input power is 15-30v DC, as the oscillator circuit is fed from an independent LM7812 linear supply.
Provision is also made on the PCB for attaching a 12v fan to cool the MOSFET & linear regulator.
Board initially built, with the heatsink on the linear regulator fitted. I used a panel mount potentiometer in this case as I had no multiturn 47K pots in stock.
Bottom of the PCB. The main current carrying traces have been bulked up with copper wire to help carry the potentially high currents on the MOSFET while driving a large transformer.
This board was etched using the no-peel toner transfer method, using parchement paper as the transfer medium.
Main MOSFET now fitted with a surplus heatsink from an old switchmode power supply. A Fan could be fitted to the top of this sink to cope with higher power levels.
This is the gate drive waveform while a transformer is connected, the primary is causing some ringing on the oscillator. The waveform without an attached load is a much cleaner square wave.
I obtained a waveform of the flyback secondary output by capacitively coupling the oscilloscope probe through the insulation of the HT wire. The pulses of HV can be seen with the decaying ringing of the transformer between cycles.
Corona & arc discharges at 12v input voltage.
Download the Eagle schematic files here: Flyback Driver Eagle Files (319)
Here is a home laser hair removal unit, a Rio LAHS4. Shown above is the system overview, with the laser wand & the user controls.
Main base unit popped open reveals the main PCB, with the central processor, a PIC16F628A.
Other side of the PCB is mainly populated with power supply & filtering for the logic sections.
Cracking open the laser wand reveals a stacked pair of PCBs, a main laser controller & the capacitive sensor PCB. This capacitive sensor connects to a pair of pins on the laser head & prevents operation if the unit is not held firmly against the skin.
Front of the laser diode module with the movable lens, on a pair of voice coil actuators. Very similar to the lens positioner used in any CD/DVD player pickup assembly.
The diode in this unit is an 808nm chip, with power in the 300-600mW range most likely.
Rear of the diode module, with the connections to the diode itself & the voice coil positioner for the lens.
Other side of the wand PCB, showing the capacitive sensor board on top of the main controller board. There is another CPU on the board here, which most likely communicates with the main processor in the base through a serial connection.
I can be found most days lurking on the GB3PZ Repeater
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