[0:00] I’ve been playing some more with the wireless LEDs
[0:02] that I showed off in a previous couple of videos.
[0:06] And I got to thinking, whilst playing with my DIY version,
[0:08] I wonder how many LEDs I can run off one inductor?
[0:12] So, I thought I’d give it a go.
[0:14] We’ve got a strip of breadboard and I’ve put the required inductor and capacitor to make
[0:19] the receiver circuit.
[0:21] I’m using my DIY driver circuit that consists of a ESP32 - which I’m using as an oscillator
[0:27] - if you wanted you could replace this with a 555 timer or even a signal generator.
[0:33] We’ve got a driver for the MOSFET and we’ve got the actual MOSFET.
[0:37] This switches our LC tank circuit to ground.
[0:40] You can watch the previous video on the DIY version that should have appeared up in the
[0:44] top right for full details.
[0:46] The inductor in our tank circuit is this coil of wire.
[0:49] The LC circuit is driven at around 217kHz which is the resonant frequency of the inductor
[0:55] and the standard capacitor value that I’ve chosen to match it.
[0:59] Since I’m driving my coil at around 217KHz and I’m using a 2.2mH inductor on the receiver
[1:07] I’ll need a capacitor of around 244pF.
[1:10] A 220pF capacitor is the closest standard value
[1:16] and may actually work better anyway as there will be parasitic capacitance on the LEDs.
[1:21] Let’s see how many LEDs we can power.
[1:24] So that’s one,
[1:25] two,
[1:26] three,
[1:27] four,
[1:28] five,
[1:29] six,
[1:30] seven - that’s seven green LEDs
[1:32] let’s see what happens if add a red LED.
[1:35] It lights up, but all the green LEDs have turned off - what’s going on?
[1:40] There’s a pretty straight forward explanation
[1:42] the forward voltage of my green LEDs are 3.2 volts.
[1:46] The forward voltage of the red LED is only 2.2volts.
[1:49] As soon as we add the red led in parallel to the green LEDs
[1:53] the voltage drops to 2.2 volts which is too low to turn on the green LEDs.
[1:58] Luckily we’ve got a simple solution, we’re receiving an AC signal so it has both positive
[2:04] and negative cycles.
[2:05] We can run our red LED in the opposite direction to the green LEDs and they will both look
[2:10] like they have lit up.
[2:11] They are just running on opposite cycles, but the frequency is so high we don’t notice.
[2:17] I’ve added another 6 red leds which makes 13 - unlucky for some, but it’s a lucky coincidence
[2:23] for us as it matches the number of LEDs on my christmas PCBs.
[2:27] I got these PCBs made up by PCBWay the channel sponsor - I’ve got a simple video on the design
[2:33] and layout process for these that you can watch later if you’re interested.
[2:36] But, let’s answer the question how many LEDs we can light up - I could just keep adding
[2:41] more discrete LEDs, but honestly life is a bit too short and I’ll run out of space on
[2:46] my breadboard pretty quickly.
[2:49] What I do have this strip of 12 volt LEDs - they do have current limiting resistors, but let’s
[2:54] give it a go and see what happens.
[2:57] You’ll notice that I’ve ommited the capacitor in this circuit - the LED strip has quite
[3:03] a lot of parasitic capacitance already - I measured it at around 190pF - this is close
[3:09] enough to the required value so we don’t need to add any extra capacitance.
[3:14] Amazingly it actually lights up!
[3:16] There are about 120 LEDs in this strip and they have currently limiting resistors that
[3:21] will be using up some of the power that could be driving more LEDs.
[3:25] Unfortunately I don’t have any more LED strips to test with - but this just goes to show
[3:30] how amazing LEDs are - they will light up with only a tiny amount of current.
[3:35] Anyway, I guess the answer to the question of how many LEDs can we drive from one inductor
[3:39] is: a lot of LEDs…
[3:42] So, back to our Christmas tree PCBs - I think we can make a completely wireless version
[3:48] of it that will look pretty cool.
[3:50] There’s a couple of things to do - we aren’t going to need any current limiting resistors
[3:54] - we’ll be driving the LEDs directly from the receiver circuit.
[3:58] So I’m going to bridge over the resistors with some bits of wire.
[4:02] We also need to make sure we put the green LEDs in the opposite direction to the red
[4:06] LEDs.
[4:07] To make it easy for me to remeber I’m soldering the green LEDs in first and putting the long
[4:13] leg of the LED into the square hole.
[4:15] I’ll solder one pin and then make sure the LEDs are nice and flat against the circuit
[4:20] board.
[4:21] For the red LEDs I’m putting the long lead in the round hole.
[4:25] Hopefully this means that I won’t mess it up and put one in the wrong way round.
[4:29] If I do mess this up it’s going to be quite hard to debug.
[4:33] With everything soldered up we just need to attach the inductor to the base along with
[4:37] the capacitor.
[4:38] One really nice thing is that the inductor is fairly heavy so we should be able to get
[4:42] the Christmas tree to balance upright.
[4:46] With it all done we’ve got our wireless Christmas tree!
[4:48] It’s surprisingly bright and works really well.
[4:51] In fact, it works so well I made another one!
[4:55] Pretty soon I’ll have a forest of glowing Christmas trees.
[4:58] I’ve linked to the previous two videos on wireless LEDs that go into more detail on
[5:02] how they work and how you can make your own, but I think that might be it for wireless
[5:07] LEDs for now.
[5:08] Though who knows, I might get some more inspiration before Christmas comes.