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GRT Dimming and Backup

L

lr172

Well Known Member
I was rethinking the b/u wiring strategy for my mini the other day. I have a separate 5ah battery to feed my HXr and mini. This helps me keep the blue side up in IFR if I have a catastrophic elec failure and also lets me shed some power from the main batt.

I am using an external rheostat for the display dimming and realized that I didn't bring the backup battery to that dimmer circuit. If I lost the main batt feed, the GRT's would go dark and I would be required to remember the button presses necessary for the dimming function, which I don't remember as I don't use them. I am not even sure the manual dimming function would work when set up for external dimming, but I thought I read somewhere that it can override the external.

Just thought I would share with others. Each power feed arrangement for the GRT's will require including the GRT dimmer circuit, if it is used.

Larry
 
Last edited:
Hello Larry,

The power failure modes is definitely something that needs to get careful attention in an IFR airplane.

Having the powered external pot would need to be protected against a power loss condition. You are definitely right, it is an easy thing to overlook but is an
important consideration.

There is an alternative for the HX, HXr and EX analog inputs. The analog inputs on theses units have user programmable 4.75K ohm pullup resistors. This means that the screen will default to full brightness in case the wire goes open. To dim, simply wire your potentiometer or rheostat to ground and to the selected input and enable "Analog Input Pullup". Increasing the resistance will increase the brightness. The scaling of the potentiometer/rheostat won't be linear, but the scaling is user settable using the "External Dimming Scale" in the Set Menu> General Setup page. The scaling will allow you finely tune the brightness vs rotational position of the potentiometer/rheostat.

The scaling of the analog input dimmer function may be useful even if you provide an external power source if the brightness vs rotation isn't quite what you want. You can finely tune it in that case as well.

-Marc Robertson
Project Manager
GRT Avionics
 
Reckoner said:
Hello Larry,

The power failure modes is definitely something that needs to get careful attention in an IFR airplane.

Having the powered external pot would need to be protected against a power loss condition. You are definitely right, it is an easy thing to overlook but is an
important consideration.

There is an alternative for the HX, HXr and EX analog inputs. The analog inputs on theses units have user programmable 4.75K ohm pullup resistors. This means that the screen will default to full brightness in case the wire goes open. To dim, simply wire your potentiometer or rheostat to ground and to the selected input and enable "Analog Input Pullup". Increasing the resistance will increase the brightness. The scaling of the potentiometer/rheostat won't be linear, but the scaling is user settable using the "External Dimming Scale" in the Set Menu> General Setup page. The scaling will allow you finely tune the brightness vs rotational position of the potentiometer/rheostat.

The scaling of the analog input dimmer function may be useful even if you provide an external power source if the brightness vs rotation isn't quite what you want. You can finely tune it in that case as well.

-Marc Robertson
Project Manager
GRT Avionics
Click to expand...

Thanks Mark! That is a good idea and I will set that up.

Larry
 
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