ESP32 Big filament clock

Inspired by one of Big Clive's YouTube videos (see here), I fancied doing something with the LED "filaments" you can get from AliExpress. 

I fancy making a big 7-segment display clock. 

Some where duly ordered up, and arrived some time later.

Now they need around 47V to light... and (allegedly) 30mA , but experiments show they are more than bright enough at 3.3mA for our purposes...

So, let's make a clock display!

Problem no 1: The power supply. 

Unlike Clive, I'm not going to run the clock off rectified mains ... I did contemplate a capacitive dropper, but, again, it's not safe. 

A quick dig about in the junque box did provide a couple of suitable transformers... one with 18-0-18 and one with 15-0-15, with 220V primaries. As we are normally somewhat above 220V here, and the secondary will very lightly loaded, these would probably do, and some tests are run. Getting an low voltage output to run the micro will mean another transformer ...

The I though about using one of the ebay buck-boost modules... except for they top out at 35V .... or do they?

Now the module is based on the LM2577_ADJ. Shown here in it's boost configuration. R1 on the module is a 10K multi-turn pot, and R2 is a fixed 360 ohm resistor.  

The output voltage is controlled by the feedback pin, so that the feedback pin is always at 1.2V. The module differs from the schematic shown here, as it has two inductors to allow for buck and boost operation, but the voltage feedback section remains the same.

 A quick calculation shows that making that resistor 250 ohms would give us an output voltage of 50V. The existing R1 is removed... 

... and replaced with a 220 ohm resistor soldered to the rear. 220 ohms will allow us some adjustment. 

The output capacitor is removed, as it's only got a 35V rating.

... it's replaced with a 100uF 63V part.

The module is powered up and adjusted for 50V

And a filament is tested. The unit is being powered from 5V, useful, as I can power the whole thing from a 5V wall wart. 

To keep power consumption down a bit, I'm going to multiplex the display. It also reduces the wiring somewhat. Each of the 4 digits of the clock will have it's own anode supply, with only one digit ever lit at a time. This allows us to connect each of the segment's cathodes together. 

The anodes will require a high-side drive, that will happily hold off our 50V. After looking around in the transistor box, it looks like a 2N7000 will do. It's a 60V FET. We'll need two per drive. I've got a load of them, and they're cheap. 

The micro's 3.3V high signal comes in via the 10K resistor, and switches on the lower 2N7000. This removes the gate signal from the upper 2N7000, and removes the anode's supply. The two resistors (100K and 47K) are there as a potential divider, so we do not exceed the maximum gate-to-source voltage of 20V. We'll need to remember the logic is inversed, input of high turns the output low, but we can sort this in software. 

It's built up and tested on a breadboard. 

For the cathode drive, we can use our old friend the ULN2003 (just, it's rated to a maximum of 50V... we could have used individual transistors again, say the 2N7000... anything rated to 50V would have done) 

The micro's inputs come into pins 1-7 and the output to each cathode via it's own 1K current limiting resistor. 

Excellent.

We'll use the ESP32, as we can utilise it's Wifi to get the current time via NTP, and it has it's own RTC. It's proved excellent in the ESP32 analogue clock. 

The end schematic is rather simple. I've added switches for wifi reset (more about that later) and 12/24 hours, and an output to drive the colon separator between the hours and minutes.

I did contemplate a PCB... but it's quite simple, so it's implemented on a piece of perfboard.

So, how to mount the filaments? 

Fusion 360 is fired up, and a design created. 

It's just a bit too large for my 3D printer, but it should be OK... 

I did have to scale it slightly to fit on my Anycubic Mega S, a friend of mine has a Pursia, and he rekons it'll fit on that if this works out too small. Anyway, it's printed, and sanded back to get rid of any lines, and painted with a little high-build primer. 

and finally finished in a bit of satin black. 

The LEDs are tested on the bench supply, some are intermittently faulty, or just dead.

Each filament gets a couple of wires soldered to each end, and threaded into the back... 

Much tea later ... 

The filaments are quite fragile, and I lost a few along the way... 

A couple of warm white LEDs are inserted to form the colon, and everything sealed into place with a dab of RTV. 

The whole thing is wired up ... each digit's anodes are connected together, and each segments cathodes are connected together..

What a rats nest !

The software owes a lot to the ESP32 analogue clock from earlier in the year. It still uses NTP to acquire the time, and uses the ESP's in built RTC. The new parts are a software multiplexer for the display... it goes like this....

1. All anodes off.

2. Set cathodes.

3. Switch on one anode.

... and repeat until the display is complete. It's identical in principle to the display driver for the STD305D turntable The ESP32 is more than capable of doing this faster than the eye can make out (in fact, it's capable of doing it FASTER than circuitry can switch the LEDs on, so there's a delay in the programme to slow it down!), so it just looks like the whole display is lit. 

The other nice bit about the software is the use of the WiFiManager library, which gives us an easy way to connect to wifi without all that tedious hard coding. That's also why I've provided a reset button, which erases the WiFi credentials, and resets the unit, so you can add a new SSID, if yours changes or you move the clock to another location with a different SSID.

Power consumption of the running clock is a bit over 250mA 

The software, as usual can be found on my git, along with the 3D model for the back panel. 

https://github.com/andydoswell/filamentclock

WiFi Manager in use ...

Just for fun, I did run one of the filaments at 30mA just to see what would happen... 

It was incredibly bright ... and lasted for about 30 mins before starting to flicker, eventually going open circuit after another 20 minutes.