Two or more 7 seg LED displays - "solder" workaround

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mackowiakp
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Two or more 7 seg LED displays - "solder" workaround

#1 Post by mackowiakp » 08 Oct 2019, 10:02

Below diagram how to connect two TM1637 7 segment LED displays to nodeMCU. If anybody interested - welcome.
7segment.gif
7segment.gif (9.84 KiB) Viewed 329 times
Displays are powered from 5V because they are blue. Brightness of blue displays is too low when powered 3.3v.
Resistor R1 (2,2k) and transistor T1 are not necessary when displays powered 3,3V (did not test it).
Transistors are BC547, diodes - any germanium "glass" small one. Please notice that in this case, transistors works both as a part of mux and as voltage level shiftier.
Pull-up resistors on CLK and DIO are not necessary because they are already solder on displays PCB.
It is necessary to use GPIO10, because it is set to "high" by hardware. before ESPeasy boot. This "shorts" DIO inputs of displays so initialization sequence goes to both displays. After boot set GPIO10 to "low" from rule. GPIOa and GPIOb can be any with default (hardware set) low state before ESP boot.
GPIOc and GPIOd - any as defined in device setup as a CLK and DIO.

Now, setting GPIOa or GPIOb to "high" gives possibility to write content to the first or second display.
Of course it is possible to use IC MUX instead transistors and I try to do this. But I shorten something, destroying IC MUX. Bipolar transistors are more "foolproof"

Tested with three 4 digit 7 segment LED displays (does not have another), using attached firmware. This FW based on mega-20190926 (normal) core 2.6.0 with small modification as described here (especially last post):

https://github.com/letscontrolit/ESPEasy/issues/2190

Changes in this FW, specifically in the 7D driver, are intended to not display zero if it occurs as a first digit in time or date. One may like it and not others. I didn't like it - so I changed.

But still there is a problem with proper display temperature in range -1C to +1C. No leading zero except temperature 0.0C. I dig in 7D driver without positive result so far. Maybe anybody else can do this work?
Attachments
firmware_2-6-0.zip
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mackowiakp
Normal user
Posts: 160
Joined: 07 Jun 2018, 06:47
Location: Gdynia/Poland

Re: Two or more 7 seg LED displays - "solder" workaround

#2 Post by mackowiakp » 11 Oct 2019, 12:50

Finally I found out solution for proper display temperature in range -1C to +1C. It works for 4 digit 7 segment LED display TM1637.
Details in github. Link in upper post

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