Solar panel doubling

 A bit of data logging showed a single 1W panel useful for supplementing battery power to my mesh network node, but not really enough to charge it meaningfully at the same time. My garden is south facing and the house blocks direct sun lots of the day so it was only the few hours where the panel was in strong direct sun that the result was acceptable. For something that spends a lot of the time asleep this would be reasonable but as I want each node to run for all the waking hours then I need it to do better. I did get 52 hours of runtime, which is technically enough for my needs if I fit two 18650s in the node, but I still don't like the thought of it running down constantly with only a tiny amount of headroom.

The data also shows the regulator board I took out of a drawer is an LDO, not a buck converter, so it's 60% efficient a lot of the time. I will make a pin compatible replacement with the converter I specified for the final boards and that should be a big help.

I've now set up two 1W panels in parallel to make an effective 2W panel. Only a few hours later it's clear this makes a massive difference as they spend lots of time charging the cell rather than just 'treading water'. I'll leave the test to run until the battery protection kicks in at 3.5V but it looks like 2W panels really are what's needed even if I were to replace the LDO. There are some really quite affordable 2W 5.5V cells on Banggood, so going up in size isn't a big deal.

Solar charger data logging


 After a little fiddling around today I had software on ESP8285 node so I can keep track of the battery use and how well the MCP73871 manages things.

Working at my desk it seems to seamlessly charge then swap over to battery if needed, but more importantly if there's roughly 0.5W charging capacity, which is what I'm expecting from the solar panels I have, available it'll run the ESP8285 and use excess to top up the single 18650 I've fitted for now. This is exactly what I was hoping for from the chip, but what's not clear yet is how well it works around dawn and dusk. Playing around with my bench PSU would give me some idea but with solar cells varying voltage under load I've just gone straight for a practical test.

The code I've put on isn't anything like the final application but it does sit there connected to WiFi pushing data to MQTT every 30s so it's a pretty reasonable test. I'm dropping the output into a .csv file on my server and I'll look at it periodically to see how the battery fares. As I wanted real timestamps on the data I used the quite nice ezTime library to sync with NTP but more importantly maintain a usable time based off the ESP8285's internal clock and only periodically update it. This is a feature I will need when things happen for real, although I'll probably have to use GPS and a local NTP server due to lack of guaranteed internet access.

Also Blogger has changed and all my layouts are broken. Sigh.

Solar charging ESP-Now BATMAN prototype

Putting a 'production' board together rekindled my interest in a solar charging prototype of my mesh network nodes.

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.

ESP-Now BATMAN boards

Back in February I was faced with a looming deadline for our LARP in March where we would be using my ESP-Now mesh network for messaging between props and also to end devices used by players.

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.

I had previously tried designing boards in KiCAD but found the interface impenetrable even for simple things and got deterred. For these boards I tried out JLCPCB's own web based EDA software, EasyEDA and was pleasantly surprised.

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.

Creality automatic spotlights

A while back I wired both my Creality 3D printers so that they are powered on and off through Octoprint. This is useful because I work two floors away from the printers and perhaps more importantly because it switches the printer off after a long print.

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.

ESP32-CAM helmet camera, prototype 1


It's been a while since I've blogged. Back in March I was working very hard indeed on making props for our upcoming LARP. With the pandemic we suddenly had to postpone until some indeterminate time in the future.

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.

Mesh networked computer terminals with RFID logon - part 6

Going back a few weeks I was having trouble with stability of the RFID readers. Which I've now fixed with a far less complicated solution.

The library has an option to turn the RFID antenna on and off. Simply shutting it off and turning back on to check the card periodically seems a 100% stable solution.

Obviously you should also check the card hasn't been swapped by checking the ID hasn't changed but here is a a minimal sketch to do this. As checking for a card stops it appearing as new it's easy to get the logic messed up but this is a tested and working example.

Note to self: start putting stuff on GutHub.


#include <SPI.h>
#include <MFRC522.h>

const uint8_t SS_PIN = D8;    //My example code is for a WeMos D1 mini, change these to match your setup
const uint8_t RST_PIN = D0;   //My example code is for a WeMos D1 mini, change these to match your setup
 
MFRC522 rfid(SS_PIN, RST_PIN);

bool cardPresentWhenLastChecked = false;
bool antennaEnabled = true;
uint32_t cardCheckTimer = 0;

void setup()
  Serial.begin(115200);
  SPI.begin();
  rfid.PCD_Init();
  Serial.println(F("Checking for RFID card removal"));
}
 
void loop()
{
  if(millis() > cardCheckTimer)
  {
    //Start a check of the card
    if(antennaEnabled == false)
    {
        //Turn the antenna back on
        rfid.PCD_AntennaOn();
        antennaEnabled = true;
        //It takes time to wake up the RFID card so the sketch needs to wait before checking for it
        cardCheckTimer = millis() + 20ul;
    }
    else if(antennaEnabled == true)
    {
      if(millis() > cardCheckTimer)
      {
        //Check for a card after a delay for it to power up
        if(rfid.PICC_IsNewCardPresent() == true)
        {
          if(cardPresentWhenLastChecked == false)
          {
            //Card was absent but has been presented
            Serial.println(F("Card presented"));
            cardPresentWhenLastChecked = true;
          }
        }
        else if(rfid.PICC_IsNewCardPresent() == false && cardPresentWhenLastChecked == true)
        {
          //The card was present but has been removed
          Serial.println("Card removed");
          cardPresentWhenLastChecked = false;
        }
        //Switch off the antenna, otherwise the card will not show as 'new' when checked again
        rfid.PCD_AntennaOff();
        antennaEnabled = false;
        //Wait before checking the card again
        cardCheckTimer = millis() + 100ul;
      }
    }
  }
}

Ender 2 magnetic bed upgrade

I'm still down the prop mines so can't post much without spoilers, but as alluded to I've been doing a lot of  3D printing again recently. The Ender 2 is great but the bed material was getting nasty and it's always been a pain to get things off as it's not removable.
My Ender 3 has a basic removable, flexible bed which is so much nicer. You can't get Ender 2 removable beds easily but you can for the Ender 3, very cheaply. This is a magnetic one which avoids any clips and as I have a second I may upgrade the Ender 3.
I assumed the bed would cut down easily to go on the Ender 2. Which has a tiny bed compared to almost any modern printer. I popped the bed off the printer, which is dead easy, marked it out with some tape and it cut easily with a nice sharp craft knife.
You can see how small the Ender 2 bed is compared to the not huge Ender 3. I wandered a tiny bit with the craft knife despite running it against as steel edge, but once on the printer it's not a problem as you'd never deliberately print that close to the edge of the bed.
Just running off my first test print now but after some faff re-levelling the bed, which is tiresome on an Ender 2, things look very promising.

Update: The small surface area makes for quite weak attraction with the base. Tall prints, especially, seem to cause the bed to slip and kill the print. I've fixed this with a couple of clips. So I've still got a removable bed it's just not an instant off one. Which is not exactly a hardship.