Any use for these component holes in the AXE133Y circuit card?

#1
I'm trying to understand the possible uses of the component holes colored red in the attached photo of the board that comes with the AXE133Y kit, in case I could take advantage of them somehow. Can anyone enlighten me? The two uncolored header holes just adjacent also seem to have no purpose, but appear to match holes in the Winstar OLED board that connects. Any application for these?
 
#3
Those holes are for backlight control on LCDs that are equipped with one, and are fully documented in my blog entry AXE133 Backlight Control.
Thank you! I'm interested in activating the dimming capability of the Winstar OLED board; I think I need to free up a pwm pin on the 18M2 for the purpose, and I believe that either location A or K is the connection I need to use to activate the feature on the Winstar (after moving the shorting SMD device on the Winstar board).

If anyone knows of an easier way to control the dimming that doesn't involve using PWM to adjust voltage I'd like to hear of it.
 

nick12ab

Senior Member
#4
Thank you! I'm interested in activating the dimming capability of the Winstar OLED board; I think I need to free up a pwm pin on the 18M2 for the purpose, and I believe that either location A or K is the connection I need to use to activate the feature on the Winstar (after moving the shorting SMD device on the Winstar board).
The connection required is pin 3, which can be easily done by connecting the wiper pad of the potentiometer (which is not fitted) to the PICAXE pin you want to use for brightness control.

Unfortunately the only pwmout-supporting pins are on portB, but the DAC is on portC.

See my blog entry - Winstar OLED Brightness Control - Version 2 - now using LCD Contrast pin
 
#5
The connection required is pin 3, which can be easily done by connecting the wiper pad of the potentiometer (which is not fitted) to the PICAXE pin you want to use for brightness control.

Unfortunately the only pwmout-supporting pins are on portB, but the DAC is on portC.

See my blog entry - Winstar OLED Brightness Control - Version 2 - now using LCD Contrast pin
I have looked at your blog entry before; I have never used the DAC for anything yet, but from reading other's experience, it doesn't seem to deliver enough current to do much without some kind of buffer. Do you feel that the DAC will deliver enough current to handle the voltage requirement here?
 

nick12ab

Senior Member
#6
I have looked at your blog entry before; I have never used the DAC for anything yet, but from reading other's experience, it doesn't seem to deliver enough current to do much without some kind of buffer. Do you feel that the DAC will deliver enough current to handle the voltage requirement here?
I've not tested the DAC with or measured the current consumed by pin 3 of the OLED but the brightness control worked fine with high-value potentiometers so it didn't need much current.

The voltage on pin 3 only needs to go up to about 1V, so even if the DAC can't supply enough current for pin 3 of the OLED without the voltage sagging, it should be OK.
 

nick12ab

Senior Member
#7
Since knowing whether or not the DAC can be used with the OLED brightness control is useful as it enables easy addition of one to the AXE033, I tried it for myself. The voltages below were measured when using the 20x4 OLED included with the AXE034.

[TABLE="width: 500"]
[TR]
[TD]DAC level
[/TD]
[TD]Voltage with OLED
[/TD]
[TD]Voltage without OLED
[/TD]
[/TR]
[TR]
[TD]31
[/TD]
[TD]4.82
[/TD]
[TD]4.83
[/TD]
[/TR]
[TR]
[TD]15
[/TD]
[TD]2.46
[/TD]
[TD]2.33
[/TD]
[/TR]
[TR]
[TD]0
[/TD]
[TD]0.05
[/TD]
[TD]0.00
[/TD]
[/TR]
[/TABLE]

The narrow voltage range over which the brightness changes combined with the low resolution of the DAC means that there are only about 6 to 10 different brightness levels (depending on display and supply voltage) that can be set using the DAC.

On the AXE132, you can add the connection between C.2 and pin 3 of the OLED by adding a wire between the wiper pad of the potentiometer (don't fit the potentiometer) and the pin marked '4' in my blog entry.
 
#10
It occurs to me -- since a location for a trimmer pot is present, how about a simple bright/dimmed selection by the Picaxe with the level of dimming controlled by the potentiometer? Perhaps feed the top of the trimmer from a Picaxe pin that goes simply high or low, and let the user set the trimmer to control the voltage output delivered to the OLED module when the Picaxe pin is high? That way, a user could adjust the dim position to the level preferred?
 
#11
It occurs to me -- since a location for a trimmer pot is present, how about a simple bright/dimmed selection by the Picaxe with the level of dimming controlled by the potentiometer? Perhaps feed the top of the trimmer from a Picaxe pin that goes simply high or low, and let the user set the trimmer to control the voltage output delivered to the OLED module when the Picaxe pin is high? That way, a user could adjust the dim position to the level preferred?
That should work.
 
#12
This is driving me a little crazy. I'm trying to figure out how to attach the high side of the trimmer to the Picaxe control pin which I guess involves cutting a trace to +5, but it looks like there is no good place to do that because there is a +5 connection from the trimmer to the OLED module, also. Do I have that right?

I've attached a photo of the AXE133 board for reference, both sides . . .
 
#13
This is driving me a little crazy. I'm trying to figure out how to attach the high side of the trimmer to the Picaxe control pin which I guess involves cutting a trace to +5, but it looks like there is no good place to do that because there is a +5 connection from the trimmer to the OLED module, also. Do I have that right?
The best approach is to bend out the leg of the potentiometer that normally connects to 5V (the one nearest the PICAXE) and run a wire to it, leaving the original 5V pad unconnected.
 
#14
Why was the pot fitted in the 1st place - no need at all with an oled module. Just chop it off or unsolder.

Connect what would have been the wiper to c.2 (that's what I did to try it).

Neil
 
#15
Why was the pot fitted in the 1st place - no need at all with an oled module. Just chop it off or unsolder.

Connect what would have been the wiper to c.2 (that's what I did to try it).
The OP wants full/dim brightness control only with a potentiometer to control what the dim brightness is. If they connect a digital output to one end of the pot track and leave the other end and wiper connected as they would be normally for an LCD, adjusting the pot will adjust the brightness achieved when the digital output is high.
 
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