Gp32 Flu Brightness Control!

[lek]

After reading the thread about MashMod's GP32 dimmer chip a while ago, I thought I'd have a go at producing a simpler method of FLU brightness control, namely using a potentiometer.

The results are more than I expected!

Using a small 1K pot, I can now adjust the brightness of my FLU from full to very low. Pics below, might post a vid later on (when it gets dark) showing it in action.

as you can see, I've placed it on the opposite side to the FLU switch.

Originally I was gonna use a pot that had a built in switch, and do away with the normal FLU switch altogether, alas I couldn't get the exact one I needed. I like what I have now even better though (Esp. as it cost < £2 to make!)

 

[sammster001]

very nice

 

[Gruntfuggly]

Lets have a pic of the insides.

Also, people shouldn't think that dimming the FLU will extend battery life - the variable resistor will just use up the rest (unless I've forgotten all my electronics)...

 

[phoda]

Actually, adding a resistor will increase battery life. Battery life is reversely proportional to the power consumed (P), which is a function of current (I) and voltage (V), where P=V*I. By adding a resistor in series with the light you decrease load, current decreases on the whole circuit, power consumption decreases and battery life increases.
And by the way that's why you call this variable resistor a "potentiometer" - a component used to control the potency / power consumption of a circuit - which is exactly what lek has done.

 

[lek]

Internal pic, the pot has been set up so that turning it clockwise will increase the brightness (so one of it's legs is bent away).

The pot is a Bourn's 3310C-102. I couldn't get the bushingless version (one without the screw threads often found on pots) so had to carefully saw the bushing off (otherwise the pot wouldn't fit inside), then saw the shaft down so it wasn't too long.

It's held in place by Loctite Repair Express Power Putty, you can mould it with your hands to any shape, and it sets solid within 1 hour (fully set in 24 hours).

Either of the wires that go to the switch can be used for attaching to the pot.

 

[Gruntfuggly]

I don't really mean to have an argument, but your definition doesn't make sense - a potentiometer acts as a 'potential divider' ie it varies the amount of resistance that is being included in the circuit. That just means that the more resistance, the dimmer the display will be, but the more power that will be disipated by the resistor - the overall power in the circuit will be the same, as the overall voltage will be the same and the overall current will be the same. How can the pot 'magically' reduce the amount of power being consumed? All it does is use some of the power in the variable resistor, instead of allowing it all to be used by the FLU...

Or maybe I'm talking complete crap...

 

[lek]

The pot is allowing less current through, not disapating it, thus battery life is extended as there is less draw on the battery (with a dimmer light).

 

[Gruntfuggly]

But how does it 'let' less current through without disipating it via the resistor? If the pot is in series with the FLU then you can only increase the overall resistance, surely?

 

[loki666]

Gruntfuggly: i think you should review your electronics...
resistances does decrease power consumption...

simple example... you put a shortcut (r=0 ohm) between your batteries and you kill them in 5min...(with huge thermal loses)
you put a huge resistor (let say ~r=1M ohm) and you batteries can hold for years...(whitout any thermal loses)
so... resitors decrease power comsuption CQFD

but your right... the overal resistance is increased
it just sucks less the batteries because of the increased resistance

 

[Gruntfuggly]

Aha - now I understand - told you I was talking crap! I guess an even more obvious way of putting it is that if the FLU isn't connected to the battery, the resistance is effectively infinite and the battery will last for ever (in a perfect world) Doh!

Apologies to all, but thanks for clarifying it in my head

 

[nerd of nerds]

hmmm... i may do something like that to my diy flu...pretty sweet!

 

[beef]

Very nice. You also have the same mouse & mouse pad as me.

 

[reeced]

Great Idea, but I think by using a higher value log pot you could just replace the switch altogether. With a higher value the current consumption would be negligible when it's turned right down i.e. the FLU would effectively be off.

 

[phoda]

an even more obvious way of putting it is that if the FLU isn't connected to the battery, the resistance is effectively infinite and the battery will last for ever (in a perfect world)

You nailed it right there. End of lesson.

 

[lek]

Great Idea, but I think by using a higher value log pot you could just replace the switch altogether. With a higher value the current consumption would be negligible when it's turned right down i.e. the FLU would effectively be off.

I did originally try a higher value pot (10k). The problem is, because the pot turns within a limited ark, you end up with, say, 10k resistance within ~360 degrees. This gives a massive gap of turning where the FLU is basically not on at all, as it doesnt take much resistance to make is go completely dark (~900 Ohms).

A 1k pot is enough to give a good sweep of brightness in the 360 degree turn of the pot, hence I really wanted one with a switch as well, but couldn't find anywhere to get the model I wanted within the UK.

Very nice. You also have the same mouse & mouse pad as me.

Heh, I must get an MX510 (red of course) to replace it soon...

http://www.logitech.com/index.cfm/products...,CONTENTID=8070

 

[reeced]

Great Idea, but I think by using a higher value log pot you could just replace the switch altogether. With a higher value the current consumption would be negligible when it's turned right down i.e. the FLU would effectively be off.

I did originally try a higher value pot (10k). The problem is, because the pot turns within a limited ark, you end up with, say, 10k resistance within ~360 degrees. This gives a massive gap of turning where the FLU is basically not on at all, as it doesnt take much resistance to make is go completely dark (~900 Ohms).

A 1k pot is enough to give a good sweep of brightness in the 360 degree turn of the pot, hence I really wanted one with a switch as well, but couldn't find anywhere to get the model I wanted within the UK.

Very nice. You also have the same mouse & mouse pad as me.

Heh, I must get an MX510 (red of course) to replace it soon...

http://www.logitech.com/index.cfm/products...,CONTENTID=8070

That's why I suggested a LOG pot.
With a logarithmic pot (commonly used for audio) the log of the resistance is proportional to the travel which means that for a significant portion of the travel of say a 10K log pot the resistance will be low, and then towards the end of the travel the resistance will shoot up - effectively turning the FLU off.

 

[lek]

Oops, didn't see you'd said log in your previous post, yeah, log pot would work well for turning the FLU "off". Depends on what you want I guess, I quite like being able to set the brightness and have a separate switch for powering the FLU, but having switch and brightness control in one is v.nice as well.

One thing I did notice is that trying to remove the gunk that holds the FLU switch in place is tricky. It sort of scrapes/chips off, but its rock solid (not sure what it actually is, some sort of industrial hardening gloop - not red or green Gloop that is!).

Maybe it could be disolved somehow for those wanting to replace the switch.