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[Dj Task Manager]

Hello folks,
Im building a sequencer device which has an LED and a relay in series with each other, the circuit is closed when a stylus makes a contact to the leg of the LED.  The relay is non polarised and the polarity of the circuit can be inverted so that the flow of current can go through a different LED instead.  There is also a pair of 1000uf capacitors in parallel (in opposing polarities) with the relay to smooth the response from the stylus .  

The problem im having is the LEDs seem to light every time but the relay doesnt always trigger.  Is this because there isnt enough current flowing through the LEDs?  If so do i need beefier LEDs? or maybe a pair of LEDs (in the same polarity) in parallel? Or do I actually need to do some maths and put a resistor in somewhere?

Other bits on my sequencer are here : mpanimation.blogspot.co.uk

Thanks!!!

[Gordonjcp]

The LEDs can only safely pass 10mA without damage, but the relay coil needs 100mA and around 5V across it to pull in.  Your circuit pretty much won't work as drawn.

What you need is a transistor to drive the relay with the very tiny current that can be pulled through the LED.  Look for articles on using relays with Arduinos and the like to give you some ideas.

[Dj Task Manager]

thanks gordon, it does sort of work at the moment but I guess the LEDs will burn out really quickly.  
Maybe I'll invest in some 100ma LEDs to solve the problem...  
I dont think I can easily make a circuit with transitors as part of the function of the devices requires the polarity to be reversed to select a second sequenced pattern.  I'll include a photo of the device later so you can get a better idea of how it works...

(also I'll take your advice and look for info about arduinos and Relays)

Cheers

[Dj Task Manager]

Hiiii, here is the sequencing machine: Mikes mechanical sequencer

I tried the configureation in the picture below on a bread board to try let some current bypass the LEDs a bit to help.  It seemed to probably be helping because with the resistors in place the LED lit less fiercely (with either one of the resistors removed the relay did not latch, so i guess it was sharing the current between both routes),

Ive just realised that I might as well put the supply voltage up to 7 or 7.5v, that might help too...

Am I on the/a right track?

[Gordonjcp]

100mA LEDs would be in laser eye surgery territory!  I'm still not quite clear on what you're trying to do.  If you just want the LED to light when you touch the wire to show that the corresponding relay is closed, you could just wire each string to each relay and wire each LED in parallel with the relay coil with a suitable series resistor (around 800 ohms, for 12v)

[Dj Task Manager]

Hi gordon, yup I think you are right, they might well scorch my eyes out!  Ive discovered that you can also get 'grain of rice' bulbs at 100ma, which although I'd have to attach to diodes to get the desired result would be a solution (and would also fit with the analoguey aesthetic of the project).

The diagram is just a simplified drawing of what is effectively happening inside my sequencing machine (IN THE VIDEO). 

What the LEDs do:  The LEDs are modified into little pegs with one leg up (to form a hook to hook onto the horizontal rods (which represent an octave on the sequencer)) and the other leg hanging down to contacted by the moving vertical rods on the conveyor which pass underneath.  A bit like programming a step sequencer on the computer but without steps and the length of a musical phrase dictated by a revolution of the conveyor; an electro-mechanical stepless sequencer.

I know its a bit of a weird project, i hope this helps make it clearer!

Thanks again for your input!

[Gordonjcp]

You can't put anything in series with the relay coils or the LEDs.

Your idea looks great and I look forward to seeing and hearing it working, but before you get there you're going to have to take the time to learn a bit of basic electronics.  Poking at stuff randomly and trying to guess isn't going to do it.

[Dj Task Manager]

Do you think using the 'Grain of Rice bulbs' (6v 100ma) will work in place of the LEDs?

[Dj Task Manager]

the idea with the resistors was to do a sort of divider:
http://en.wikipedia.org/wiki/Current_divider