"MAR3501" 3.5" LCD with touch - but no connectors for touch? - Page 1
Forum section: electronics / general

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: May 03, 2020, 03:02:44 pm
content: I got a display from ebay, SKU "MAR3501". According to the seller, and this page, this "have touch". And indeed, a touch panel is mounted.http://www.lcdwiki.com/3.5inch_Arduino_Display-UNOThe display is glued to the board with doubly adhesive foamy stuff, I am reluctant to tear it off and wreck it to see where the extra flex cable for the touch panel actually goes.But from what I see in the pinout on that page, there are no connections for the touch panel or a controller that might hide somewhere, and only the ILI9486 chip is mentioned, which, last time I checked, does only TFT stuff, not touch.The ICs in the foto of the bottom side are 2 pieces 245 line driver ICs and 1 LDO.So what is this? A cultural difference in spec brief expectations, e.g. "we only say have touch, no say can use, hahahaha!",or am I just missing something?

author: mikerj
author_rank: Super Contributor
timestamp: May 03, 2020, 03:25:18 pm
content: If you look in the demo code in the lcdwiki link you provided, there is are examples for reading the touchscreen. They appear to be multiplexing the LCD chip select and address/data mode pins (A2, A3), i.e. switching them to analogue inputs, reading touchscreen values and then switching back to digital outputs for LCD control.Seems a little dodgy doing this with the chip select pin though. It's a little surprising this isn't stated in the documentation which is actually pretty good compared to many Chinese modules.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: May 03, 2020, 03:29:52 pm
content: Quote from: mikerj on May 03, 2020, 03:25:18 pmLOL! Good catch.And true to all that.I don't really like that, it's too messy, I guess I'll get another one which explicitly mentions the touch IC used.It's only for a little weekend prototype thing... but stlll.

author: jackthomson43
author_rank: Contributor
timestamp: May 04, 2020, 04:40:35 am
content: As you are going to buy a new one, so I would recommend you to buy 7 inch TFT LCD. It's bigger in size thus gives a professional look to the project and it's not that costly. Btw why don't you use simple LCD, check outLCD 16x2 Pinout, it will help.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: May 04, 2020, 06:11:42 pm
content: Quote from: jackthomson43 on May 04, 2020, 04:40:35 amYour crystal ball must be malfunctioning, as my not at all described project does not require such a big screenI wouldn't mind a very slight size increase to 4", but 3.5" seem more common for a good price.Those with 5" then jump to roughly double the resolution I'd have to deal with. I don't need higher resolution, so it's a burden.Somewhat (but not a lot) greater touch area than 3.5" would be nice, but I think this will do.I just have zero extra patience for dealing with the ramifications of this silly design choice that is this funky pin mux'ing described by mikerj,hence I rather buy the "proper model" with an XPT something touch IC on it for a whopping 2 bucks more, which I would have bought in the first place, had I been aware of this...

author: amyk
author_rank: Super Contributor
timestamp: May 05, 2020, 04:55:55 am
content: Quote from: TinkeringSteve on May 03, 2020, 03:29:52 pmIt's a resistive touchscreen, so no IC.

author: hansd
author_rank: Contributor
timestamp: May 05, 2020, 11:51:05 am
content: https://www.waveshare.com/product/displays/lcd-oled/lcd-oled-2.htmHave a look at this. They have an resistive touchscreen interface chip.