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GPS Clock Brightness Difference Between Display Drivers
maczrool Posted: 12 Jan 2021, 03:01 PM
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When building the clock, I inadvertently bent one of the leads and soldered the whole thing in. I attempted to bend the lead into the hole but it ended up snapping off so I ordered a replacement at Digikey. This one works fine, but runs its half of the display noticeably brighter than the other driver that came with the kit. This variation is especially noticeable in dark conditions. Is this just a matter of variation between batches? I’d really like the two halves to match in intensity.

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mit Posted: 12 Jan 2021, 11:01 PM
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yeah whatever

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Unfortunately the brightness is a function of the current gain of the driver chip. Like the hFE of any transistor, this has a nominal gain value, but will vary wildly between batches.

The easiest thing to do is to replace both driver chips at the same time, if you ordered more than one from digikey then replacing the other driver might be enough.

It would technically be possible to add more resistors to the current mirror circuit to be able to adjust their relative brightnesses, but given how the board is laid out it would be very tricky. Easiest to just replace both drivers I think.

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maczrool Posted: 13 Jan 2021, 04:01 PM
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Thanks for the reply. That’s kind of what I figured. I just ordered one, but my concern being that even if purchased at the same time, I may get different batches with different characteristics. Such are the perils of DIY electronics I suppose!

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