Hop up tracer unit project

[Svendogg]

One for the techy guys more than anything I think...... Gonna have a go at making my own hop up tracer unit, to go in my G&G Raider 2.0, I'm planning on wiring it to the main battery tamiya connector. Planning to use a pair of 3.2v UV LEDs for this - I'm aware I'll have to use a resistor to limit the forward voltage. Question I have is am I going to have issues with power surges as the motor fires up? Will I have to also use some sort of diode as a protective measure? What's the simplest way to run the wiring? What size cable should I use?Has anyone got experience doing this?

[simonh]

I’ve done a load of these and I always wire to a separate battery, it is just easier and I am fairly convinced that by have the led lit all the time energises the bb’s a bit better. I used to do 2 LEDs each side of the hop but the last one I did was just two on one side, it was easier to wire and should last a bit longer on the 9v battery I pair them with.

 

worth noting that there is a new tracer hop recently released that only costs about £30 and should fit most m4 receivers

Some examples

[Svendogg]

Thanks Simon. Going to take your advice and go for a separate battery pack, going to use a couple of 3v cr2032 cells, which I reckon I can wire to the front and install within the handguard in a way that I can still access the switch. Plus this will make it easier for splitting the receiver in future. Planning to use 3x UV LEDs with 3.6v forward voltage, individually throttled down via 120 ohm resistor. Should be able to get decent brightness and run time, and keep it small and simple. Cost of parts should be less than a tenner, including the "prototype" hop unit 

[simonh]

Sounds like a decent plan, have you calculated the run time with the 2032’s? I get about 3 hours with a 9v

[Svendogg]

I haven't calculated it - ideally want to mock up the circuit first and check the current it actually pulls, but based on the LEDs having a typical draw of 20mA and peak of 30mA (as per the eBay sellers description, who knows if that's accurate) and the 2032s being 225mA (ish) it should be a couple of hours at least I'd have thought. If it is going to make significant difference then I may scale it back to 2 LEDs, but would need to recalculate the resistor values. Would you mind sharing the setup of your circuit?

[simonh]

https://store.brightcomponents.co.uk/product/10x-3mm-uv-purple-flat-top-ultra-bright-led-10-pieces/
 

these are the LEDs I use, my circuit is super simple positive to positive neg to neg, resistors on the negative leg. If you speak with bright components they will give you a circuit and resistor values depending on what power source you intend on using. You can buy the resistors from there as well

 

Simon

[Svendogg]

Thanka for that Simon thats an awesome resource, can definitely see me buying from them in future. 

 

I've done a quick calc and I reckon I'm looking at about 3hours continuous run time from 2x cr2032 batteries..... How that works in practice with volt drop we'll see 😁 

[Rogerborg]

Last time I knocked one up, I used a 3.6V (well, 3.4V - 4.2V) 18650 cell, and a small value resistor.