Suggestions for a small panel to display a 2-digit number - Page 1
Forum section: electronics / beginners

author: Youkai
author_rank: Regular Contributor
timestamp: November 10, 2023, 02:24:06 am
content: I'm working on a "countdown timer" thing and I need to display the amount of time that it's set for (in minutes). Minimum requirement is to show a two digit number. If it can do 4-digits so I can show minutes and seconds as it counts down that might be nice but is not required.My first thought was to use a 7-segment display. A quick look at Youtube convinced me I don't want to use a "raw" 7-segment because that's way too many pins to deal with. I also saw a video using a TM1637 which seems to be a "time" 7-sedgment display that uses 2 data pins. That seems much better. I also know that little LCD panels are an option.Please provide suggestions on good, inexpensive, options for this use case. If you can order the thing on Adafruit or Sparkfun that's a bonus but not required. Thank you.

author: ataradov
author_rank: Super Contributor
timestamp: November 10, 2023, 02:47:17 am
content: What dimensions for a digit you are looking for?4 digits requires 7+4 = 11 pins. Unless you are already using a ton of pins, it may be worth getting a bigger MCU. If this is just a timer with a display and a few buttons, the Arduino should be able to handle that.And using standard segment displays would give you a huge range of options for size and color.

author: themadhippy
author_rank: Super Contributor
timestamp: November 10, 2023, 02:59:36 am
content: If you've got i2c available maybe the HT16K33 ,available either with or without 4 7 segments already fitted

author: radiolistener
author_rank: Super Contributor
timestamp: November 10, 2023, 03:42:41 am
content: just buy some OLED microdisplay on aliexpress, it cost about 1 USD and allows to display 128x32 or 128x128. You can show about 2x16 or even 4x16 symbols with your font...Something like this one:https://www.aliexpress.com/item/32672229793.htmlI'm using it to display temperature, pressure and humidity from BME280 module, it allows to show all things on display + pressure change simultaneously. Also it is often used to display some info in different diy projects, like automatic antenna tuner, etc.Since this is graphics display, you can draw 7 segment digits or whatever you want. But I'm using usual font. It requires just 4 wires: +3.3V, GND for power and SCL, SDA for communication from MCU. Works pretty fast, you can update entire picture many times per second

author: Youkai
author_rank: Regular Contributor
timestamp: November 10, 2023, 04:38:50 am
content: I've got a Sparkfun Pro Micro already so the plan would be to use that if possible. That has I2C so anything using I2C can work.

author: ataradov
author_rank: Super Contributor
timestamp: November 10, 2023, 04:44:14 am
content: Well, those 128x32 OLED modules are I2C. If the character size works, use them.

author: DavidAlfa
author_rank: Super Contributor
timestamp: November 10, 2023, 04:47:31 am
content: 1.3" OLEDs are cheap and easy to interface.

author: kjr18
author_rank: Regular Contributor
timestamp: November 10, 2023, 12:25:20 pm
content: Well, you could use one of these:https://www.aliexpress.com/item/4000126673475.htmlThey are cheap and easy to use. As they use two 74HC595, you could simply use shiftOut function, or use some libraries to do it for you, for examplehereis one that I sometimes use. Only 3 pins needed.

author: sparkydog
author_rank: Regular Contributor
timestamp: November 10, 2023, 05:35:53 pm
content: Adafruit has a selection of four-digit 7-segment displays with I²C drivers.

author: MarkT
author_rank: Frequent Contributor
timestamp: November 11, 2023, 08:28:33 pm
content: I reckon the easiest to interface to is a serial display like the COM-11441 (sparkfun), but there are cheaper displays

author: EPAIII
author_rank: Super Contributor
timestamp: November 12, 2023, 06:16:07 am
content: I don't understand why this is even a problem. There is a multitude of LCD, OLED, and even LED displays with serial inputs. They need only two pins from a Arduino, PIC, or other processor: serial data and clock. And they can display one, two, or even four lines of text, each up to 20 or more characters long. Seconds would be no problem as the clock can be the processor clock rate. And some can even display graphics.https://www.google.com/search?client=firefox-b-1-d&q=serial+LCD+display

author: themadhippy
author_rank: Super Contributor
timestamp: November 12, 2023, 12:45:43 pm
content: Quoteyou know that, i know that,but not everybody does,so whats wrong with asking for a pointer in the right direction?

author: soldar
author_rank: Super Contributor
timestamp: November 12, 2023, 01:44:07 pm
content: Is this even worth building?You can find many different countdown timers on eBay for under $10.

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: November 13, 2023, 03:07:50 am
content: A Max 7219 and a couple 7-bit LED displays will do it. The 7219 requires a two wire SPI and a chip select and will drive up to 8 digits. They are available pre assembled off Amazon for about $3 each.

author: Youkai
author_rank: Regular Contributor
timestamp: November 27, 2023, 04:19:48 am
content: I'm thinking about getting these:https://www.amazon.com/Self-Luminous-Display-Compatible-Arduino-Raspberry/dp/B09JWN8K99/ref=sr_1_6?keywords=OLED%2BArduino&qid=1701058179&sr=8-6&th=1They will give me a little more flexability in what I display and getting some practice with I2C OLED would probably be good for future projects. My only concern is that it says "There are no fonts embedded". Is that a normal thing? I didn't see anything in the couple youtube tutorials I found that talked about explicitly embedding a font. Do the standard libraries have a default font embedded already?

author: ataradov
author_rank: Super Contributor
timestamp: November 27, 2023, 04:30:57 am
content: This is a graphical display, not a character display . You get to draw whatever characters you want. Libraries would often have fonts included.

author: Whales
author_rank: Super Contributor
timestamp: November 27, 2023, 04:40:47 am
content: Quote from: soldar on November 12, 2023, 01:44:07 pmAfter having used several timers from eBay and alix: I'd say yes, they all suck in annoying ways. I'm all for OP to do this.Previous model: very bad battery contacts, kept having to clean them all the time. Completely unsuited to being anywhere near a kitchen.Current model: takes a AAA battery (yay) but cost more and reacts weirdly to button presses sometimes. Often restarts when you want them to stop, requiring more button presses (and often erasing your previously entered time).

author: Youkai
author_rank: Regular Contributor
timestamp: November 27, 2023, 05:01:26 am
content: Quote from: soldar on November 12, 2023, 01:44:07 pmIf all I wanted to have was a simple countdown it wouldn't be. A kitchen/egg timer or my smartphone would be much better. But in this case I'm building a version of this which uses an LED strip to do the countdown. My wife is a 3rd grade teacher and she said this would be great in her classroom.

author: Youkai
author_rank: Regular Contributor
timestamp: November 27, 2023, 05:08:58 am
content: Quote from: ataradov on November 27, 2023, 04:30:57 amI see. Thank you for that information. I did another search and found acharacter display.What would you say are the main differences that and thegraphical display. It seems like it's roughly the same price as the graphical display. I'd be using it with a Sparkfun Pro Micro. Will the both work with that fine? Is the library for the graphical display significantly larger since it has to contain a font?I guess all things being equal I'd prefer the graphical display since it seems more flexible. Are they close enough to the "same thing" that it doesn't matter much which I use?

author: ataradov
author_rank: Super Contributor
timestamp: November 27, 2023, 05:11:33 am
content: Quote from: Youkai on November 27, 2023, 05:08:58 amThis is the same graphic display, just a bit lower resolution. It uses the same controller.Don't worry about drawing characters, libraries take care of this.

author: radiolistener
author_rank: Super Contributor
timestamp: November 27, 2023, 06:37:42 am
content: Quote from: Youkai on November 27, 2023, 05:08:58 amThis is the same display, just different resolution, it has more pixels width but less pixels height