Diming the 7-segment gear display

[gui67]

Hello Lance,

i use the 7-segment indicator as gear display as decribed in your documentation:
http://www.msgpio.com/manuals/mshift/index.html

It works well. I have added the decimal point to show lock-up function.
However, it is a little too bright for night driving.
I would like to know if it is possible to dim the leds either with a potentiometer, by reducing supply voltage, or in a different way.
There is certainly something, but I do not understand the documentation when it speaks about the LE, BL and LT inputs. I think diming is related to LE, but I don't know how to use it.
Could you give some precisions?

Thanks in advance
Guillaume

[Bernard Fife]

Guillaume,

Increasing the resistance of R1 thru R7 will reduce the brightness (the brightness depends on the current through the LED which in turn is set by the current limiting resistors). You could also reduce the supply voltage, perhaps by using Vref at 5V instead of the suggested 12V supply.

Lance.

[Matt Cramer]

Another possibility would be to put a potentiometer on the supply voltage side.

From a code standpoint, could they be PWM'ed in response to a switch input?

[gui67]

Thanks Lance for your answer, I did not think about increasing the individual resistors. I was only thinking about complicated solutions like PWM...

Another possibility would be to put a potentiometer on the supply voltage side.

From a code standpoint, could they be PWM'ed in response to a switch input?

Matt, I first thought that this might have had an impact on the function of the led driver, but as I read the spec again, it seems that it functions with supply voltage between 3 and 20V. So I will try to supply it with the dash light voltage, that is adjustable with a potentiometer.
I will just have to check if I use 12V or 5V as power supply and change the resistors if needed.

The PWM solution is nice too: I use the Small CAN Dash Gauge from James, which has the possibility to adjust brightness and has 2 levels depending on the light signal. I might be able to use a signal from this gauge to control the same brightness on the Gear Display. How is the brightness controlled with PWM? should it be just wired to the LE pin? Is there a need to use a specific frequency?

[Bernard Fife]

How is the brightness controlled with PWM? should it be just wired to the LE pin? Is there a need to use a specific frequency?

Guillaume,

Yes, the PWM dimming signal goes to the LE pin on the HFC4511. The supply voltage can be anything from a few volts up to the supply voltage, but no greater. There is no specific frequency required, but it needs to be fast enough not to flicker (> 30 Hz or so) so that it isn't annoying to the eyes, and generally should be less than 1 MHz (which you are unlikely to feed it anyhow!).

Lance.