Contrast on LCD

[vasa]

Hi there – thank you for sharing this excellent product!

I just finished building my kit… 1.4u. I am currently only powering it via USB.

Everything seems to be working fine but the contrast on the LCD is bad. The text is there but you can only read the screen at very low angles… looking straight at it I only see bright rectangles.

Any tips on where to look for a problem? Maybe I should throw a pot on instead of RLED?

[Ray]

Make sure your RLED is 100 ohm. There many resistors in the kit but there is only one that’s 100 ohm. If it’s correct, please measure the voltage between LCD’s VO pin (3rd pin from the left) and GND (1st pin). Let me know the voltage reading.

[vasa]

Thanks for the quick reply.

On close inspection my RLED is marked brown-black-gold. My meter is reading 1.2 Ohms (in circuit). The instructions didn’t specify a band pattern for RLED and I used the process of elimination… it was the last resistor left so I just soldered it in 😆 . I guess I should have looked more closely. I used every resistor in the kit and I just triple checked every other resistor and they all look fine. Definitely not a 100 ohm anywhere.

So I guess the wrong resistor got thrown in the kit… off by 1 color band.

[Ray]

The ring colors of a 100 ohm resistor should be brown-black-brown. Sorry if it’s missing from your kit. What you have soldered onto RLED right now is one of the two 1 ohm resistors. These two 1 ohm resistors are supposed to go to Rsc (but as explained in the instructions, one of them is optional). Please double check the Rsc resistors: if you have soldered both, I am pretty sure one of them is the 100 ohm you are looking for. If it’s not there, I am happy to send you one tomorrow.

[vasa]

Bingo.

My meter was not showing Rsc at 100 Ohms but I had my wife use her younger eyes to look at the bands and it does indeed look like I swapped RLED and Rsc as you described. My bad (eyes)! 🙄

[Ray]

Cool, glad that you found it. Just be careful desoldering components.

[vasa]

Problem solved… I desoldered the improperly installed resistors and put correct ones in… working perfectly now.

One question… I’ve left the device turned on with no load for a couple of hours and it is noticeably warm by now. The probe on my meter is saying 75F… which is maybe 5 degrees above the ambient temperature in the room. Is this normal?

EDIT: I taped my probe to the case with painters tape and it leveled off at 77F

[Ray]

That’s normal. The switching regulator and the Ethernet controller both dissipate considerable amount of power during operation, so they will feel noticeably warm.

[vasa]

Cool. Thanks again for providing an excellent kit and support… I’m looking forward to deploying it in my yard this spring.

[Author]

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