Hi,
I have an adafruit liquid crystal light valve (lclv), which I want to drive with the arduino gpios (should be OK, draws a small amount of current). The lclv has only 2 input pins (vcc, gnd).
The thing is I want to switch between "positive" and "negative" voltages for the lclv (the manufacturer stated that it is fine).
Will connecting the lclv to 2 gpios, and setting them to High/low accordingly, work? Or is there some backdraw to this configurarion?
Thanks in advance
unameuname:
Hi,I have an adafruit liquid crystal light valve (lclv), which I want to drive with the arduino gpios (should be OK, draws a small amount of current). The lclv has only 2 input pins (vcc, gnd).
The thing is I want to switch between "positive" and "negative" voltages for the lclv (the manufacturer stated that it is fine).Will connecting the lclv to 2 gpios, and setting them to High/low accordingly, work? Or is there some backdraw to this configurarion?
Thanks in advance
I have one of those in my Harbor Freight welding helmet.
Your plan cannot produce AC. You can produce AC square wave from ONE output pin if you can find a 1:1 pulse transformer and drive one side with the Arduino square wave. The other side will be the AC square wave.
But what are you trying to accomplish?
Paul
There are 6 pwm pins, I intend to use 2 of them as the pins described above. (and, for example, with 50% duty cycle for the vcc pin I can achieve the square wave).
I'm not 100% sure I fully understood the problem you stated, mind clarifying it a bit more?
As for the intention -
I want the liquid crystal to act as a voltage controlled quarter-wave plate, (can be achieved when +-2.5v are applied)
The Arduino pins can only be +5 or 0 volts relative to ground. There is nothing you can do to make a pin do a negative to ground.
The transformer eliminates the ground as both sides of the transformer are insulated from ground and gives you the alternating signal you want.
There are plenty of pulse transformers for the major distributors. I see them on some of the boards we build, but I don't know what the boards are doing.
Paul
The Adafruit product page makes no mention of negative voltages on the electronic shutter. 5V and 0V switches it completely.
However, if the shutter is to be opaque for long periods, they do refer to using an AC square wave drive, as described in this note.
You can do that by connecting the display Vcc and GND to two output pins that rapidly alternate between 1 and 0, effectively producing an AC signal.
unameuname:
Hi,I have an adafruit liquid crystal light valve (lclv), which I want to drive with the arduino gpios (should be OK, draws a small amount of current). The lclv has only 2 input pins (vcc, gnd).
The thing is I want to switch between "positive" and "negative" voltages for the lclv (the manufacturer stated that it is fine).Will connecting the lclv to 2 gpios, and setting them to High/low accordingly, work? Or is there some backdraw to this configurarion?
Thanks in advance
No, that's exactly what you need to do, drive in antiphase from two pins.
jremington:
The Adafruit product page makes no mention of negative voltages on the electronic shutter. 5V and 0V switches it completely.
Apart from the text highlighted in blue:
If you're going to turn it on (make opaque) for more than a few minutes, use an AC square wave between the two pins to avoid a DC bias that can damage it.
Its just a bog standard transmissive LCD display with one large pixel, all the standard issues of
driving LCDs apply. EEVBlog has a great video about driving LCDs somewhere.
As I stated, if you bother to read past the first line of the post.
jremington:
As I stated, if you bother to read past the first line of the post.
That's not my point, you mis-represented the Adafruit page - they clearly state use AC for long period use,
even highlight the warning in colour.
No, I did not misrepresent the Adafruit page. Not sure what your problem is.
The more I think about the OP's original post, I think he is correct. The whole purpose of the AC is to keep the crystals stirred up in the liquid and switching polarity that way would do it with no other components.
Paul
Hi,
Dave EEVblog on static LCD driving.
Tom.. 