A small solar cell in typical UK weather is not going to be able to run the node 100% of the daytime, but it will almost certainly work as a useful 'runtime extender'.
I started looking at this way back last autumn then like a lot of things my enthusiasm waned and it languished in a box for months. Today I finished off putting it together to a point where I could knock some software up and start logging charging/load data.
I'm using the same ESP8285 module I have for the nodes, with an MCP73871 development board for charging and power management. The naive approach would be to stick a conventional LiPo charger in parallel with the batteries but the load messes with the charging.
The MCP73871 manages the power path so that depending on the charging power available it will run the load from that while also charging the batteries, run the load from it, or once it it is too low run the load from the batteries. As the battery isn't directly connected to the load this can be done while maintaining proper charge behaviour for the LiPo. It is not proper MPPT tracking for the solar cell, but it does sensing of how much current it can draw before the voltage drops too low that will have a similar effect. For extra efficiency a DC-DC converter that does MPPT would help, but I'm going to suck it and see if this prototype is 'good enough'.
I've shoehorned several INA219 current/voltage sensors into the power path so I know the battery, charging and load detail. My plan is to stick this inside my shed, with a solar cell outside and simply log the data until it falls off the network because the MCP73871 has decided to protect the battery.
For this to work we'd need some fixed nodes to give minimal coverage. I had previously built ten static nodes using Wemos D1 mini Pro boards and NiMH batteries and used them in testing but battery life was only around eight hours which wouldn't be enough even with overnight charging.
I did a few sums, came up with a power budget and figured something with a more efficient regulator, no indicator LEDs and a couple of 18650 cells in parallel should easily run for a whole weekend, eliminating another point of stress for the game.
Scratch building all this would have been a drag so I designed and ordered twenty boards from JLCPCB in China.
While I did have a bit of a struggle finding matching footprints for the components involved the process really wasn't hard. They also integrate this fairly tightly with the PCB ordering making the generation of gerber files, drill files and so on something you don't need to worry about too much.
This smoothing over of the complicated process meant I was able to get to grips with EasyEDA, design a board and order it in a morning with my only previous experience being a couple of failed attempts to do something useful in KiCAD.
Sadly with the postponement of our game due to the pandemic these boards have sat on the side since delivery but today I finally built one and it works! I added a reset switch to make repeated programming easier, and were I to design them again I would add a reset and flash button on the board, but for now these suffice. There's almost nothing to the circuit, it's an ESP8285 module, buck regulator, battery holders and some headers. No charging or protection circuit and nothing to leech power that isn't needed.
Until I add more features I have in mind like onboard solar charging then they'll do. In the meantime I'll do some current measurements and rundown tests with this one to check its performance. I'm really hoping these will give us the coverage we need for the game and now I've some more time to work on it I can actually check properly.
Coincidentally somebody from the LARP community asked me to see if I can make a design that takes four AA batteries and I put this new version together. The 6V from the battery pack works much better than the single 18650 and means they can be swapped easily but sadly makes the camera really quite bulky. Nonetheless I've sent them the files so they can have a go at building some units.
Going forward I've seen that the LDL1117 LDO only has a 0.3-0.6v dropout and is pin compatible. I think carefully desoldering the AMS117 and replacing it with one of these would solve my brownout problems.
An alternative would be a small 'daughterboard' that connects to the headers and has a buck convertor. This would be the more elegant option, especially if I managed to include the power switch and lamp button onboard. I've still not found time to see if I can make an I2S microphone work with the board, but that could also go on a 'daughterboard' if it did.
Then I put quite a lot of effort into painting it up in a basic camouflage pattern. I am very pleased with how this worked out.
No other real changes to the project but it shows you can make something decent looking at a low cost.
This has been working perfectly but I often have the light in my cellar switched off making the camera monitor pretty useless unless I go and switch the light on.
I figured it stood to reason that switching some lighting on with the printers was a good idea and I made up a couple of little spotlights attached to the printer frames and connected them to the same SSRs that switch the printer power.
The spotlights are made from some ceramic GU10 bulb holders I had, 20mm electrical conduit and some 3D printed parts I quickly knocked up in OpenSCAD. I knew from my work with making fittings for GU5.3 12v bulbs that heat from the bulb wouldn't be an issue with the printed parts, they barely get warm to the touch even after several hours.
I only did this yesterday but it's already meant I haven't been leaving the cellar light on as much while working on projects.
This killed my enthusiasm for a bit and when I picked up projects again I needed a change.
Over the last couple of weeks I've been fiddling with the ESP32-CAM board again and turned the pile of components in the first photo into a working helmet camera prototype.
With the standard camera example code loaded it works really quite solidly and the battery life with a 18650 cell recovered from an old laptop battery pack seems good.
I started out with the selfie lens for aesthetic reasons but it does a good job of taking in a whole room as you move around, something the default lens these boards ship with doesn't do.
The tactile button on the side switches on the onboard 'flash' LED and there's an acrylic light pipe bringing the light out of the shadow of the lens. It's not a proper long throw torch but it just about manages to light a dark room so you can see and the camera will generate a very grainy picture with the gain up full.
Onboard charging is nice but currently getting the cell in/out in the field is impractically fiddly and the holder is stuck in with tape. The indicator LEDs on the TP4056 board are brought out on the side with another couple of light pipes and these work great. The idea is if these were issued on a multi-day game it would be the player responsibility to keep them charged and a USB charging socket makes that practical. For a short game they probably won't need charging.
Overall this has worked out really nicely and the design I've done in OpenSCAD is modular enough it's easy to swap out the rail mount and add something different. These could easily double as 'CCTV' cameras with a ball socket mount.
The design does need a little more work to make it easy to assemble but broadly it's there. I've also had it suggested that an external antenna would be acceptable, when I thought it would be too ugly. So I'll work on a version with that over the next few weeks, the boards have a uFL connector and it'll really help increase range.
I've got enough camera boards and recovered batteries in good condition to build a set for a whole team of 'marines' and a few static CCTV units. Doing this while keeping the cost down for 10+ units has been a major requirement of this project and I've definitely succeeded at that. The bill of materials using the recovered 18650s comes in at about £7 plus printer filament at the moment.