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Forum Index : Microcontroller and PC projects : ILI9481 display
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| f2cf1g Newbie  Joined: 18/11/2016 Location: United KingdomPosts: 13 |
Hi everybody. I have a 9481 display working with a 28 pin Micromite, thanks to matherp. The drain is very heavy for a battery powered project, does the device provide a means for controlling the backlight current? I have looked at Rpi LCD connectors and there is no mention. |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
The backlight current can be a killer on many a battery project, so I hear what you are saying there. You could do what I have done in a few projects, and use an I/O pin to switch the LCD backlight off and on via a couple of transistors:  This is NOT my design, it was found on the net and tweaked using the help of the members here, but it is now my go-to design if I need a high-side switch for anything, and have used it not just for LED backlights, but also to turn off RF modules etc that don't have a SLEEP command or pin, to save standby current. Just about any NPN transistor will work, but you need to choose a MOSFET with a Vgs voltage that can handle the supply voltage you are going to power the backlight from. I have used this on several projects now, and it works great. If you wanted to get fancy, you could use a PWM output rather then just an off/on I/O pin, and the PWM would allow you to control the brightness. You could even fade the backlight in and out if you wanted to get really sexy.  Smoke makes things work. When the smoke gets out, it stops! |
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TassyJim Guru  Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
On most displays, the backlight can be controlled using PWM. It needs a bit of external hardware. PWM is easy to do on the micromites and will be an option if the display controller doesn't have builtin control methods. Jim Edit Grogster beat me to it. VK7JH MMedit |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Sorry......  Smoke makes things work. When the smoke gets out, it stops! |
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Azure Guru Joined: 09/11/2017 Location: AustraliaPosts: 446 |
The ILI9481 does not have any functions to control the backlight, it does have power saving modes but these are for driving the chip and LCD pixels. Your main power saving is as Grogster and TassyJim already mentioned, controlling the backlight power. This is done on the MM+ LCD backpacks (as a build option) using a circuit like Grogster mentions to drive the display on/off or via PWM to control brightness and therefor lower power consumption. I have found the power saving using PWM is significant and the lower backlight brightness for normal viewing is quite good. |
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| erbp Senior Member  Joined: 03/05/2016 Location: AustraliaPosts: 195 |
The use of external circuitry as suggested only works if the LCD being used has a separate pin on the I/O connector for backlight power. In the case of the 4" IPS ILI9481 (see this thread) which I think may be the type being referred to, the backlight power connection seems to be internal to the LCD PCB, thus not giving any opportunity to provide external control over it - either just on/off or PWM brightness control. Phil. |
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| Azure Guru Joined: 09/11/2017 Location: AustraliaPosts: 446 |
It would assist members in supplying more useful help if you provided a link to the display you are using. |
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| f2cf1g Newbie Joined: 18/11/2016 Location: United KingdomPosts: 13 |
Thanks for the replies. Some background. I have a system (weather station) working with a 9341 display exactly per the MM manual. It has a separate power line to the backlight so I use a high side switch similar to the one cited by Grogster above to switch off the backlight power after a period of inactivity. It is switched on again by touching the screen. I am in the process of upgrading the display to an ILI9481, specifically the one identified by Phil above. I understand the use of PWM to dim the screen and save power but I don't understand how that would work with only the one power line that the ILI9481 appears to provide. Surely the controller won't work if its power is being cycled? My suspicion now is that the only way to cut power consumption is to switch the LCD module off but that this will disable the touch function too. If that's the case I can live with it, just means adding a mechanical button to reactivate. Roy |
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