Development board LDO upgrade

During my work on the helmet camera project, I found that I was having a few brownout issues and occasional flakiness. At some point I found out that the 'low dropout' 3.3V regulator used on the ESP32-CAM development boards has a minimum dropout of 1V.

That's not a hugely uncommon minimum dropout but simple maths shows that a LiPo putting out a realistic 3.8-4.0V in use is not going to result in 3.3V supply to the board.

I put a multimeter on the Vout of the AMS1117 on an ESP32-CAM board and when in use for video streaming it was down around 2.9V.

In principle the datasheet says the ESP32 will operate at 2.3V but there are onboard 1.8V LDOs used to power PSRAM to take into account too. The datasheet recommends a 3.3V 500mA supply to the module unless you also provide separate 1.8V supply.

As it stands, the module is just not getting that from a 4.0V LiPo.

I had a look for a good solution but my component browsing failed until I was recommended the ST LDL1117S33R. It's pin-compatible with a minimum dropout of 350mV. They're not expensive parts so I took a gamble and ordered 100 as the AMS1117 seems to be the default LDO on many cheap development boards.

After a little bit of hot air rework on an ESP32-CAM to replace the LDO, I measured Vout in the same conditions and found a solid 3.25V.

While I don't know if this will help, it feels like it should improve stability under LiPo power and I know it will make a big difference to usable battery life. It has definitely cured the issue where the 'flash LED' on the ESP32-CAM would flicker while streaming and powered by a LiPo.

I may yet make a 'shield' for the ESP32-CAM that includes other components for the project and a buck convertor would be more efficient still but this is a good incremental improvement.

ESP32-CAM helmet camera, prototype 3

 

While working with the ESP32-CAM board I've realised that the AMS1117 LDO fitted to it is a bit of a problem due to a 1V dropout value. This means that if you power it from an 18650 cell it starts to brown out far sooner than needed.

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.

ESP32-CAM helmet camera, prototype 2

 

I did a little more work on the design and added an external antenna, as it's a known fact the board works better with one.

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.

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.

ESP32-CAM case, selfie lens and mount - part 1

Poundland (the major UK 'dollar store') had selfie lenses for 50p so I picked up a few to play with on my stash of ESP32-CAM modules.

I've 3D printed a mount that protects the board and lines up the lens perfectly with the existing camera. The lens is an interference fit, at least on my printer, and screws in firmly.

Initial testing seems positive as it really expands the field of view. It's never going to rival a GoPro but makes the module much more versatile. You can buy a wide angle cameras for the ESP32-CAM but typically you have to buy that separately, almost doubling the cost so this was a cheaper way to get similar effect.

It also gives it a 'big lens' look rather than the pinhole camera of the usual module. Which is the aesthetic I want.

I still need to design a back to the case but this should give me a robust housing for these things. Different backs could have different options including a battery holder and switch.

The flash LED is exposed close to the lens but this would work better with a bit of acrylic rod acting as a light pipe and make it possible to make the whole thing passably waterproof with some thought.

The nasty thing with the LED is it shares a pin with the SD card interface so if you access the card it flashes. This is a problem. I have no idea who would have thought that was a good idea, it's not like there aren't any free pins. Fine if you use the camera over the network but makes the flash useless in situations you want to write to SD and if it's battery powered will chew power. Just why?