 Power Electronics is not something that many of us have an opportunity to work on. These days, a lot of our technology is dealing with microwatts of power at very low voltages. So, a lot of engineers are unfamiliar with the basics of power electronics. And so, middle of last year, I embarked on an ongoing project to try and educate myself a bit more about the Internet of Power Electronics. And I managed to captivate the attention of Tristan, and so we, in the autumn of last year, we had two or three sessions up at Tristan's premises in north Wales, where we worked on what we are calling the open inverter. So, unfortunately, I had to spend three or four days here, and it's a very old, very low ceiling, very low door height cottage. And so, the motivation for this project was that we wanted to create an easy-to-understand, easy-to-build, low-cost, power conversion component that could be applied to a wide variety of different applications. Based on open source hardware, using easy-to-obtain components, we felt that putting a power limitation of about 250 watts on it would make it manageable. That is typically what you will get out of a large, single solar panel of about one square metre. So, typically, you might be dealing with voltages up towards about 30 volts and currents of maybe eight or ten amps, so of that order. And we felt that if we had this open inverter, it would be good to, from the start, build in the instrumentation and the monitoring that we need in order to see how it was performing. So, we wanted to build it with the monitoring built into it so that it can tie in with the open energy monitor wireless ecosystem. This is the lab area. This is the room where Tristan has been describing where his heat pump is, the indoor part of it is, located. It was very nice in September, a little bit chilly when I visited later on in the year before we had the heat pump running. So, this was the office for about three or four days and this was our 200-watt test solar panel that was placed roughly south-facing. You see it in sort of speckled shade. It did have some tree cover at a certain time of the day and as the sun went round we would move this round to get the best sun. Okay, the main system components. We've got an Arduino-based 80 Mega 1284 controller. We've got an H-bridge that's made out of N-type MOSFETs, which are the cheapest ones and we use an integrated MOSFET driver, which in our case is the Intosil HIP4082. We integrated the low power wireless energy monitor, which is the RFM69 transcever module that talks to the 80 Mega. The application, well we've got the solar panels outside, which are the less than 250 watts of output. And we decided that lithium polymer electric bike batteries would be a good way of adding modular storage. They come in a sort of little caddy that clips onto the frame of your e-bike. They have got a standard mounting connector that could easily be 3D printed. They're modular and they're about between a half and three quarters of a kilowatt hour. So you could add storage in as much as you required for your small system. Okay, I then had to go off and start to develop the building blocks for this system. So I started with my Arduino based controller, which for reasons historically is called Ynode 5. It's got the 40 pin larger brother of what is commonly used in the Arduino. That's the 80 Mega 1284, which has got 16K of RAM and 128K of flash. So you're not going to run out of either RAM or flash for your application. As I said earlier, the RFM69 low power wireless, we can plug in an ESP8266 Wi-Fi module if we want. We can plug in an optional Bluetooth low energy module. It's got a real time clock, battery powered, it's got a boost converter so we can run it on a single alkaline cell or we can run it from a lithium polymer cell. It's got micro SD card for data logging and it spits out USB using the new 50 cent USB to serial IC. The CH340G. So all that fits onto a 50 by 50 double sided PCB. Now I really wanted to have these boards to hand out today but as I speak they are just leaving the factory and I should have them tomorrow. So this is a very compact board. The 50 by 50 format has been chosen so we can make use of the very low cost offers from some of the Far Eastern board houses. It has an extension of the Arduino pin header. So you've got your digitals on this side, your analogs and then you'll see that what is normally the six pin power connector, that's extended by a further six pins and making full use of the right hand side there. Some of you may recognise an XB footprint in the middle. That's so that you can take your favourite wireless module on an XB shaped shield and plug it straight in. The RFM69 is down here. The micro SD card is on the back of the board. We can handle either the 48 pin quad flap pack or the 40 pin DIL version of the 80 mega. This header is for the ESP01 and then the eight pin top and bottom there so that we can plug in up to two of the H bridge modules and the whole thing bolts together like a sandwich. I started looking for suitable H bridge modules and this is one that's based on the Infinion BTN8960. Now these are half H bridge modules. They're really designed for the automotive product market for windscreen wiper motors, door winder motors, seat positioning motors. So they're kind of only rated up to about 18 volts but about 40 amps. These modules are available ridiculously cheap from China. That module, as you see there, is about £6 from a supplier in Hong Kong. However, after I'd blown the first two of those, I thought I'd better do something else. So I designed my own board and this started life as a low voltage power board if you can read upside down. So you've got the two modules there and they have a large rectangular heatsink flag coming out this way from the tab on the surface mount device. In its original application as a motor controller, this board quite happily works without a heatsink. Those large copper areas only get up to about 40-45 degrees C. So that's quite tame but it still has the unfortunate voltage limitation of about 18 volts. So I looked around, I proved that I could get that version of the H bridge to work in a toroidal based transformer inverter. So that's it. I've got the Arduino controller driving the H bridge with PWM, 250 watt toroid in the centre. And this is a double switch outlet that I could plug some mains equipment into. That works pretty well. So I then went on to look at a H bridge module based on discrete n-type MOSFETs, which would be easier to build. And also design into it my own over voltage, over current, over temperature monitoring. So I can shut it down if it starts to get into an undesirable area of operation. So that's your basic H bridge. You've got four MOSFETs, you've got the load strapped between the middle, and then you've got the driver chip on the left hand side there. This is a current sensing resistor and an amplifier with a gain of maybe 100, which can then go into an ADC on your microcontroller to sense what the current flowing through the H bridge is. So quite simple. Just had to implement that onto a board. I resketch that in Eagle CAD. I am separately sensing the one half of the H bridge and the other half of the H bridge with the two current sensing amplifiers. So that was reduced to one of my favourite 50x50 board layouts. And I've got one here, which I'm going to pass around. That was an early version, but that's it in the flesh. The idea being that we've got some vertically mounted heat sinks that can take the heat out of the upper and lower pairs of FETs, and this is the communication to the microcontroller. The whole thing was powered on local porthmatic brewed beer, and this was our first successful test. Tristan built up on breadboard, the discrete H bridge with the transistors and the two driver chips here. This thing glowing blue is, I think that's the Arduino controller. We have a small transformer, and this is a 40 watt filament light bulb, if I remember rightly. So we got this working at about 11 o'clock on the first or second night, and it was like magic. So after we got back from the pub, yeah, I think so. Okay, and there we put a scope across the... I think this was the drive out of the microcontroller into the H bridge, so that we could see that we were actually... No, we're on a 100 volt range, so that is actually the output from the secondary of the transformer. Okay, so applications, a micro solar inverter, panels up to 250 watts. We could store power, as I said, in e-bike battery modules. We're getting about a 90% efficiency. We could use the H bridge as a DC to DC direct power transformer, so that you don't have to invert AC and then transform and rectify back down to DC. And the modules can be parallel together for greater capacity. Here is solar powered soldering. You can just about make the smoke coming off the tip of the iron. That was from the 200 watt panel sitting out on the lawn. Okay, the wireless module, it's a 433 meg. It's compatible with the G-Labs, G-Libs, G-Nodes library, which is part of the current Open Engine Monitor system. We could plug in an ESP8266 and have it set up as a Wi-Fi access point. We could plug in a BLE module and then be able to access it from a smart phone. And one of the things that we could do is be able to turn loads on and off according to the availability of power using wireless switching. Okay, other applications. The split pi DC-DC converter. Charging of smart appliances. A DC ring main where you distribute something like 48 volts around the periphery of a room. And in each DC charging point you've got a high efficiency DC-DC converter where you can plug USB and 5 volt type charging appliances there or 20 volts for your laptop or whatever. Or also using the H-bridge as an e-bike charger or motor power controller. That's the split pi converter. As you can see it's an H-bridge. It's got a large reservoir capacitor in the middle and it's got a filter L1 and L2 on the input. But basically you can put an input voltage here. And depending on the relative duty cycle of the S1, S4 pair or the S2, S3 pair you can either boost or buck by a factor of about 5 to 1. So you put 12 volts in here and get 60 out there. Or your load at that side might be the DC motor on your e-bike and you can buck or you can boost from that side and recharge your e-bike battery on this side for regenerative braking. So the H-bridge is a fundamental component of all power electronics and very, very versatile. And that's just a cross section through a typical e-bike battery. It's made up of something like 50 of the standard 18 mill diameter 65 mill long cells. So those are now very cheaply available from our friends in China. So that's that. Thank you.