I’ve been kicking around this idea for a couple of years. I think it is time to piece it together and build it.
Specs:
Linear style Power Supply for optimum quiet/silent use.
Maximum Voltage Output 15 – 32 Volts DC perchannel
Maximum Amperes Output 3 Amps perchannel
Modular design so I can easily add more channels. The base setup would be single channel. However the Micro Controller would limit the amount of Channels to add.
Computer Controlled via RS-232 and USB or Ethernet to control it by Web Browser.
Remote Controlled (IE: TV Remote)
Most of the parts are off the shelf such as the 0-30V LM317 based power supply modules. I haven’t had one to play with but I imagine it can be modified to use a different Voltage Regulator such as the LM350 and possibly add a bigger 47Ohm Power Resistor to an higher Wattage such as 10 or 20 Watts. Replace the Filter Capacitor with something higher rated, 2200uF isn’t going to cut it for 3 Amps of output. Might also need to swap out the Diode to a beefier one as well.
A Arduino as the brains, probably a Nano to have enough IO to do what is needed. I could roll out my own and use a dip style ATMega328p but the Nano is cheap these days. Replace the Potentiometers with Motorized Linear Potentiometers, they’re pretty cheap on eBay. Now I wouldn’t want the whole supply to run off the high output so I would toss in a SMP Power Supply to control the Digital side of things. To keep things simple I’ll use Optoisolators or Relays on the Arduino Outputs to control a few things such as the Output ON/OFF function and Power the Main Transformer ON/OFF.
Theory of Operation
Digital side of things
Plain and simple. We are going to treat this kinda like a group of Computers that is connected to a KVM switch. We will have an Arduino as the Master and each Channel has a Slave Arduino. The base of the system will comprise with the SMP to run the Master Arduino that will act as a KVM switch to switch between other Slave Arduinos to Control. Each Salve will be the brains of an Output Channel. The whole purpose of each Slave is to read back the Voltage and Current, control the Motorized Potentiometers for Voltage and Current and to turn ON/OFF the output. When the Master has a shut off command it will cut the Power to the Main Output Transformer and tell all of the Slaves to return the Potentiometers back to Zero. To turn off the whole thing I will use a Soft Latching Power Switch circuit turn off the digital side.
Current Sensing
Since the Slave will be connected to the Master via the i2c Bus I need to measure the Current usage. I believe a ACS712ELCTR should do the trick. It just uses a single Analog Pin on the Arduino.
Voltage Sensing
There are many Arduino Voltage Meter projects on the Web. There was one I used that I modified to use the TVOut Library to use a old TV as the Display. It’s really a Voltage Divider that the Arduino reads. and if memory serves me right it uses Two Analog Pins from the Arduino.
Motorized Potentiometer
I haven’t played with one of these but looking at a few pictures and some quick reading I would need a Motor Driver. I’m thinking of the TB6612FNG could work. Thing is I would need one for each Motorized Potentiometer.
Analog side of things
Modify the 0-32 volt Module boards to use higher rated components for increased Current use. Each channel board will have a Heatsink for the Voltage Regulator and Power Resistor. Also have a Fan mounted to the Heatsink for added cooling.
Main Output Transformer that can output a large amount of Current. I have one pulled from a UPS that can handle 10 Amps. I highly doubt I would need multiple outputs putting out 3 Amps at one given time so this should work just fine. A terminal fuse on the Transformer and probably the heatsinks to the Channel boards.
Construction
The more I type up the more I might have to end up spinning some PCBs or build it in a way that the Module works like one of those old Tektronics Scope plugin Modules.
For the chassis I want it Rackmountable and easy to service so I can add more Modules easily. It will probably end up as a Tabletop unit. I plan to use Ribbon Cable for the digital stuff and 16 Gauge cable for the rest. So probably a Backplane to attach the Ribbon cables to so I can daisy chain the Channel Boards via i2c and maybe a backplane with Molex or T-Terminals to daisy chain the high voltage. It would be neat to construct it so it’s hot-swappable and compact the channel boards to fit in a 5.25 inch bay.
Why make it like this?
I want it modular so I can easily upgrade it without having to build a new one. Lab Power Supplies are expensive as all get out and even the el-cheapo supplies are a bit costly. If I build it like this then I would only have to spend about a hundred bucks and when time for another channel to be added or upgrade the main power transformer I can do it with $20.00 to $40.00 bucks. Not to mention if I screw up and kill a channel I don’t have to spend much time troubleshooting it.
The IT Garage 