Auto Darkening lens for welding - Where to find a circuit diagram?

[wsemajb]

I'd like to see how this ticks. I'm particularly interested in the sensors and how they integrate with the circuit. Anyone know where I might come by a schematic?

Thanks so much.

 

[blueroomelectronics]

What sensors are you talking about?

 

[Externet]

The way I did it successfuly was first applying an audio generator to the LCD shutter and varying the amplitude and frequency to find the optimal darkening setting for that particular shutter, within reasonable amplitude limits. It was around 90Hz and 15 Volts p-p.

Then built an oscillator at those exact frequency and amplitude, switched-on by a phototransistor, or a plain on/off switch if you want it manual.

Miguel

 

[wsemajb]

I don't know what the sensors on these units typically are, but let's say phototransistor. Yes, essentially I'm wondering how to augment/assist these sensors with a plain on/off switch. I don't have a clue where in the circuit would be appropriate for this.

There are anywhere between one and four sensors on a typical lens module in one of these helmets. How could you 'override' these while still maintaining the light/ir sensing function of the sensors? Switch the lens on/off manually, while using the existing sensors as fallback.

 

[Externet]

Addition of the manual switch to an existing phototransistor circuit can be placed in parallel or in series.
In parallel will force manual on but disable automatic off.
In series will disable or enable automatism from the phototransistor, but not have manual control for operation.

The placement of such manual switch would be in the battery supply circuit lead.

To "...'override' these while still maintaining the light/ir sensing function of the sensors"... would be disconnecting them from their circuit; their sensing function kept latent for other whatever-you-want use.

Miguel

 

[wsemajb]

Are you suggesting that it might be so simple as switching dc power to the unit on/off? I would just have to find the point on the board where main power is applied, since most units (including the one I'm looking at) use solar suppliment to the batteries.

How would a switch in parallel with the phototransistor be applied? The transistor itself is going to be a discrete/identifiable unit on the board with three leads (i'm guessing). If there are more than one (there are typically two or four) and they function as redundacies, then it should be sufficient to apply a switch in parallel with only one of them to force the lens dark.

 

[Externet]

Yes.
Either solar or battery or both powered, removing (manually switching off) the power will clear the shutter window.
Applying power (switching on) will darken it.

Try covering the solar cells if it has any, and removing/installing the batteries.. Should turn off/on.
Miguel

 

[Torben]

My Miller Elite mask has 4 sensors, which I believe are photodiodes. The LCD darkening is only for comfort--the plate in front of the LCD should absorb or reflect the UV regardless of whether the screen actually darkens. Still, these things are designed with speed in mind, and AFAIK, photodiodes win over phototransistors and certainly LDRs for speed.

I don't know what the fastest way to power an LCD screen on and off is, but I would think that simply switching the power rail should do it (as long as any bypass caps don't slow things down).


Just some random thoughts,

Torben

P.S. Good auto-darkening masks rock. Especially if you weld stick.