in case you want to make one too, though I’d hold off for a bit until I’ve got the little monster a little calmer in its attitude!
All that’s missing that you need to know is that the LiPo battery attached to the V4 red line, and the black GND line below it.
Drone breadboard layout
P.S. The breadboard and breadboard wire kits both came from Maplin
All of my headless projects use Lithium Ion batteries. These are made up of 1 or more battery cells which each produce 3.7V and potentially many amps in a small, light package. Their only downside is you need 5v to run a Raspberry Pi, and so need to add some form of regulator. My three projects have 3 different power requirements, and use 3 different regulator circuits which I thought I’d share:
- Turtle needs a 5V supply able to supply up to 3A for the stepper motors. This means starting with a 2 cell combination delivering 7.4V. However delivering 7.4V at 3A means 2.4V (7.4 – 5) @ 3A is wasted as heat – given it’s a recharchable battery, I don’t really want that level of waste (nor heat melting the Lego Turtle!). So the turtle uses a low drop out, switched mode regulator LM2596T-5.0 with the circuitry as suggested by the data sheet (a schottky zener diode, a couple of electrolytic capacitors and a 33uH 2.5A inductor). This has proved perfect in all but one respect – the LM2596T has 5 pins packed into a TO-220 package – that means the pins are closer that the standard 0.1″, meaning they need to be bent carefully to fit. I broke one doing so, so caveat emptor!
- SkySpy has an 11.1V LiPo (Lithium Polymer) battery to supply up to 30A to the blade motors. So the low-drop out is not needed in this case, but since the drop-out is now 6.1V at up to 1A for the Raspberry Pi, I still don’t want to waste the power; once again another switching regulator steps in: 78SR105HC. this one is not cheap, but it’s efficient, has only 3 pin (like a TO-220 plus heatsink) and lies flat on the breadboard which is critical when you have helicopter blades whizzing round.
- Finally for the SkySpy controller, this is using the same battery as the Turtle, but doesn’t need anything like the high current, so the wasted power will be minimal, so I’ve gone for a non-switched regulator (LM2940T-5.0) which has feedback circuitry to minimize the loss in high drop out situations
All of these came from Farnell as always!
A headless Turtle really needs to be tail-less too. It’s hardly free to roam with a mains lead shoved somewhere indelicate, is it? It’s been a little tricky and so costly getting this to work, so I’ll share with you the final magic ingredients…
Lithium Ion battery 7.4v 2.2AH – why?
- Even without monitor, keyboard and mouse, RPi boots and then dies without a 3.3v and 5v supply even though the 5v isn’t used for much outside the GPU
- Lithium Ion cells produce 3.7v, so you need to get a couple in series to get >5v required
- I bought 2.2Ah batteries to give me > 2 hours running the Turtle between charging
- So 7.4V 2200mAH it is, but I don’t want to just warm up the ecosystem with the extra voltage over 5v, so…
A switch mode regulator is needed as the most efficient way to convert 7.4V to 5V at up to 3A without producing 7W of heat – the 5V powers the stepper motors as well as pieces of Pi and they can draw > 1A each if they’re in a mood.
Then I need to take the 5V 3A DC, and tap off a 3.3V @ ~700mA to run the bulk of the Pi – that I used a Low Drop Out regulator as the voltage drop was 1.7V and the current < 0.7 => 1.2W heat generated – the regulator doesn’t even start to get warm.
Put that lot together and this is what you get – a well stuffed breadboard, to the extent that I bought many heat sinks and inductors while trying to find a combination that would fit on the breadboard.
TurtlePi, powered from a Lithium Ion rechargeable 7.4V battery with just WiFi to the outside world
P.S. A little logical thought (too late) meant I realised the 3.3V regulator was unnecessary. The 5V regulated from the battery was fed via the GPIO pin 2 to the RPi 3.3V regulator, thereby feeding 3.3V back to the breadboard via GPIO pin 1. Which is lucky because I was running out of breadboard lines, but this frees a couple.