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Forum Index : Microcontroller and PC projects : PM: 2.8" LCD board for the PM...

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Grogster

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Joined: 31/12/2012
Location: New Zealand
Posts: 8238
Posted: 10:02am 17 Sep 2022
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Hi all.

Cos I needed a board to drive a 2.8" SPI LCD with the PM, I came up with this board that piggy-backs onto a standard 2.8" SPI module with touch:









The board is four-layer.  Four-layer boards used to be very expensive compared to double-sided, but these days, that is not the case.  These four-layer designs cost a whole two bucks more then the standard double-sided price.  Seven bucks for five vs five bucks if it were double-sided, so it makes sense to simply go directly to four-layer if it is easier to route everything, and it is on this size.

All PM pins are routed out to a box-header.  2x3 header for 3v3 and ground connections for experimenters.  RTC module with EEPROM memory chip, HC12 wireless module, linear LDO regulator, piezo sounder and reset button all on-board.

With the aid of a daughterboard, you could easily add anything else you wanted to to the PCB stack such as the LPF for audio out or a PWM motor driver or something like that.

Needs 9v DC supply if you want to use the piezo, as they don't tend to "Start" on 5v or less, but if you KNOW you won't be using the piezo or the GUI touch click sound, then you can run the board from 5v.

EDIT: Forgot to add the OPTION TOUCH command to the silkscreen, but I will be doing that shortly.
Edited 2022-09-17 20:09 by Grogster
Smoke makes things work. When the smoke gets out, it stops!
 
Mixtel90

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Joined: 05/10/2019
Location: United Kingdom
Posts: 2975
Posted: 10:16am 17 Sep 2022
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That's very neat! I've not attempted 4-layer yet. Well, not for anything other than a bit of playing.

I'm not suggesting this as a change, but if a spare GPIO pin was available it could PWM a charge pump or even a very simple SMPS to get sufficient voltage for a piezo. As GP25 is only useful for driving the base of a transistor it might be a good use for the latter. I must look into that...
Edited 2022-09-17 20:19 by Mixtel90
Mick

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Volhout
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Joined: 05/03/2018
Location: Netherlands
Posts: 1649
Posted: 02:43pm 17 Sep 2022
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Hi Grogster,

Are you sure 3V3 is sufficient to light backlight. ? I always used 5V with a resistor.

Volhout
If nothing goes right ... turn left
 
Grogster

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Posted: 03:47am 18 Sep 2022
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Deleted your duplicate post.

I normally use 5v also, but I have hooked up an LCD and 3v3 works fine for the backlight.  At least on the 2.8" SPI LCD anyway.  Perhaps NOT on the bigger 5" or 7" LCD's, but we're not using either of those.

With a 27R series resistor, the LCD is quite bright - even on 3v3.
Smoke makes things work. When the smoke gets out, it stops!
 
palcal

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Joined: 12/10/2011
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Posts: 1553
Posted: 05:19am 18 Sep 2022
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I seem to remember there is some configuration on the back of the LCD, a 3.3v reg. to run off 5V. and it can be shorted out for 3.3V.
"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"
 
Grogster

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Posted: 05:57am 18 Sep 2022
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Yes, you are correct.  "J1" - solder-blob it to bypass the on-board 3v3 regulator and run the display from an external 3v3.  The LED connection is separate from that though.
Smoke makes things work. When the smoke gets out, it stops!
 
Glen0
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Joined: 12/10/2014
Location: New Zealand
Posts: 56
Posted: 08:34pm 18 Sep 2022
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Looks very nice thanks, I would like to get my hands on a few as soon as the board is ready. I Recall way back that there was an issue with dodgy HC-12 modules on the market. Is this still the case and if so can you suggest/recommend a supplier.
Are you expecting to stock up in the near future?
 
Grogster

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Posted: 05:55am 20 Sep 2022
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Howdy Glen.
Yes, I will be getting at least five boards to experiment on, but I could get ten boards if I know you would like some.
Yes, the dodgy HC12's are an issue.
Basically, any that are being offered for US$3 or so, are bound to be clones, so avoid those listings like the plague.
I have a contact at the factory now, and order direct from the manufacturer to ensure they are genuine.  But even the people making the HC12's are having issues with chip shortages.
I got some recently, but only a small batch, and I have them already reserved for other things which is why the website still lists them as sold-out, but if you were after a couple, I can spare a few.
Genuine ones now have the HC logo laser-engraved into the top of the crystal package.
This is something that costs money to have done, so no cloners are going to go to the cost to have that done on what seem to be rejected crystals anyway.
So, keep a close eye on the crystal on the HC12.
If it has the HC12 logo lasered into it, the module will be genuine.
Clones won't have the logo on the crystal package.

I note that with the latest HC12's I got, the MCU has changed back from a QFN package, to the SSOP that the module originally had on it.  My guess would be cos the QFN chip is hard to get at the moment, but perhaps they were able to buy stock of the SSOP chip.  These modules still have the laser-engraved HC logo on the crystal though.
Smoke makes things work. When the smoke gets out, it stops!
 
Glen0
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Joined: 12/10/2014
Location: New Zealand
Posts: 56
Posted: 10:14pm 20 Sep 2022
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Yes I am definitely keen to get some. What's the minimum number of boards you would be prepared to supply to me and roughly how much are they each?
Cheers
 
Quazee137

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Joined: 07/08/2016
Location: United States
Posts: 370
Posted: 06:49am 21 Sep 2022
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This is GREAT. Inline with a change over I have been working on.

 It'll be a good jumping off board to do some testing.

 A header cable wired to match the RPi header and test my RPi hats on the pico.
 Using the RPi 3.5" display on my testing jig but haven't got around to the 2.8"s.

 I have a board I'm working on that has the chip and not the pico board.

 Waiting for your testing of them. I'll need to make five.

 Who is your order from? JLPC    I hope.

 Thanks

Quazee137
 
Grogster

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Posted: 12:31am 22 Sep 2022
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@ Glen - Please PM me or email me and we can discuss your needs as I have not yet placed the order, so it would be the perfect time to incorporate you.  I'm not interested in profiting from this, so on-sell at cost price.  For ten boards, JLCPCB are currently charging US$7 but more will probably affect the price, so we need to talk about your needs.  Please remember that this is the 1A design - the prototype - so before you get too excited and order heaps, we probably should prove the design with a small number of test boards before you commit to a large quantity of PCB's if you catch my drift.

@ Quazee137 - Yes, I get everything through JLCPCB these days.  Assembled or not.
Smoke makes things work. When the smoke gets out, it stops!
 
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