ESP-Now BATMAN Real-time clock

I'm still slowly adding features to my retro computer terminal props and one of the things they lacked was a real-time clock.

So far I've been using 'mesh time' a millisecond uptime value that syncs across the mesh network.

I've now added the option for one or more nodes in the mesh network to share real-time clock information. This leverages the built in libraries for time that are included in the ESP8266/ESP32 SDK. It's just an offset from the mesh uptime with some simple logic to pick a preferred real-time source. Much like the mesh uptime it's not millisecond accurate, but good enough for human scale time, eg. the timestamps on chat messages. It also shares timezone information to correctly handle daylight saving.

At the moment I'm testing with SNTP (which is supported directly in the SDK) but my plan is it can take any RTC source. My code just checks "is the time set?" before sharing time so this should be trivial. this could include manually setting the clock from a watch, but I suspect it would drift fairly quickly. I'll attach some GPS modules onto a couple of my nodes for a time source in the field.

Chindōgu - part 3

I've been tempted for some time to do my planned updates to the Chindōgu, adding sound and more importantly, trying to throw together some code that avoids using Ekiga in the graphical desktop. The Pi Zero really struggles running the desktop and graphical applications but is fine when throwing stuff straight at the framebuffer.

Some research suggests it's possible to spin up OMX player wrapped in such a way it'll play a network stream straight from a camera and I'm going to try and use that for the video at least.

Coincidentally, there's currently a Hackaday retro competition and I think this could make an acceptable entry, if I get the software together and have several all talking to each other. I've accumulated multiple Sony Watchmen and Pi Zero Ws to do the build with.

To get started I've pinned out the main components on a board as it's otherwise hard to work on. One thing I want to do is get the image as decent as it can be and these horizontal gun CRTs were always dodgy.

Lacking a service manual I've worked out the function of the trimmers by trial and error.

• RV501 - Vertical size
• RV502 - Horizontal hold
• RV503 - Keystone adjustment
• RV504 - Horizontal size

Tweaking the framebuffer settings on the Pi Zero and tweaking these has made the display almost usable. With is set to 320x240 you can actually read the command line.

In praise of Adafruit IO

After a long delay on the delivery of the solar panels I want for my solar mesh nodes, I finally got around to doing some testing with them.

Unfortunately I was away from home and relying on tethering to a mobile phone for access to the Internet so using my home MQTT server for logging wasn't impossible, but was going to be inconvenient.

It occurred to me to give Adafruit IO a spin as it's designed for making generic IOT logging easy to set up.

Quick and easy to get working it has been logging just fine and I've not swapped back now I'm home. The dashboard is basic but all I need for this test.

In the first graph you can see the VPCC feature of the MCP73871 working well to avoid flatlining the voltage from the solar panel under load. It has a target voltage (arbitrarily set to ~5.3v here) and reduces current draw if the supply voltage drops below this. I've added a small trim pot to my test board to allow me to tweak this and do some runtime comparisons.

VPCC isn't MPPT but it will get better efficiency out of the panel than simply drawing until it can give no more and the voltage sags below a useful level. In the second graph you can see how without VPCC set the load on the same panel causes cycling like this, which also won't be doing the LiPo cells any good.

I have an idea ruminating to use an I2C controlled potentiometer along with a current sensor to make adjustments on the fly to try and optimise the solar output but it may be a minimal return compared to doing the tests once and picking a set value for VPCC. It will certainly increase component count.

There are packaged up MPPT solutions around, but there seems to be a gap in the market with them either super-efficient energy harvesting for tiny panels, or for large domestic/industrial power solutions. My scenario of ~4W panels with a ~100mA load isn't something I've spotted a good packaged solution for.

It wouldn't be impossible to roll my own MPPT boost convertor in front of the MCP73871 but like I said very likely to involve diminishing returns over careful use of VPCC.