Dual 4 digit 7-segment display board with SPI interface

in project logs by DP | 16 comments

Raj built a dual, 7-segment, display board with SPI interface. The board is based around the MAX7219 8x 7-segment display driver, which receives commands over SPI, and drives the display accordingly.

The new display features eight 7-segment displays arranged in two rows of four digits. The on-board MAX7219 driver enables you to easily add eight 7-segment LED displays to your project using only 3 I/O pins of microcontroller. The major advantage of using this board is the time-division multiplexing operations required for continuous refreshing of the display digits are performed by the MAX7219 chip, thereby keeping the microcontroller free for doing other pressing tasks. It is suitable for displaying two variable values simultaneously in a project, such as displaying temperature and humidity, or current and voltage, etc.

We like the idea behind this project, but with a price tag of $12+ for the MAX7219 it isn’t cheap.

Update;  Raj is selling 5 kits constituting of the PCB, displays and MAX7219 for $11.99, which is a bargain considering that just the MAX7219 is $12+ dollars in the ones at Mouser.

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Comments

  1. Pedro Diogo says:

    Like you said it’s a cool idea but for that price you can buy a low power microcontroller, write your own firmware and save $10.

    • Steve says:

      For me, my time is money. Therefore if I was doing this project as a one off, $12 isn’t so bad for a all in one package that I know works. It would take me time to wire up, code, and debug a microcontroller. On the other hand, if I needed this display for a kit I was giving out or for a run of 10 units or more; the microcontroller path would be the way I would go.

    • Raj says:

      You could probably buy a microcontroller for $2 with sufficient I/O pins and program it to drive 8 seven segment digits. But what about the cost of 8 seven segment displays, perf board, 8 transistors for multiplexing, eight base resistors, and eight current limiting resistors for each segment?

  2. James says:

    If you can find it in DIP form the Austria Micro AS1100 is a direct replacement for the MAX7219. It appears to be more readily available in SOIC-24. Likewise the AS1107 is a near drop in equivalent with just a register or two difference. I have used 1000’s of AS1107 over the years in my products. Even at 1-2 pcs they can be purchased at Digikey for $6.50 or so. In volume I pay about $3.

  3. SQKYbeaver says:

    i have a few of the max7219, i was contemplating building something similar, great job!

  4. Raj says:

    Guys,
    I am not trying to make any money by selling this kit. I have made 10 PCBs from iTeadStudio and I am just trying to give out 5 of them to those who need them. And I don’t agree with the statement that $12 is too much for this kit. You are getting a PCB, one MAX7219 IC, two 4-digit seven segment LED displays, a header connector, capacitor, resistor, and FREE SHIPPING within the continental US.

    • Pedro Diogo says:

      Not at all but reading the post you get the idea that $12 is just for the MAX7219. If $12 is for the whole kit it’s not a bad price at all.

      • Mats says:

        $11.99 for the kit is actually quite cheap considering that the DIP version of the MAX7219 is about $12 in smaller quantities from the major suppliers….

        Get >25 of them and they come down to $8 leaving only $4 for the PCB and other parts. Still a good price for the kit.

      • Steve says:

        Depends on where you source the chip. The MAX7219 at Mouser in the US is $12.28 for 1 piece. The price really drops when purchased in quantity.

      • Trev says:

        MAX7219 is down to 50c ea on eBay in DIP format

      • eff zog says:

        Its not just the 7219 that is expensive, I find seven segment displays .56 inch and above (in hobbyest quantities) haven’t come down in price since 1975 and I was buying them from radio shack! Bulk leds are certainly cheaper now – can’t understand. And back then your choice was red or off.

    • Filip says:

      Raj, the comment in the post was not aimed at the price of your kits, but at the MAX part by itself…$12 is a very good price for a kit like this..

  5. Drone says:

    These are nice for driving 8×8 single color matrix displays (need one chip per matrix then chain them).

    As for the Austria Microsystems drop-in replacement, the AS1100PL is the dip form of the chip, but it is hard to find. The AS1100WL in SOIC-24 is available for around $6.50 in unit quantity (Newark US has a promo on at $5.05 right now for unit qty.)

    The AS1106/1107 parts are not drop-in replacements for the Maxim parts, but are arguably better. Also cheaper than Maxim and similarly priced to the AS1100. The AS1106.7 are also available in PDIP-14 (hard to find) and SOIC-24.

    The AS1100 is 5V only, the AS1106/7 are 2.7-5.5V.

    I like these parts, but for small-medium runs I too would probably look to a micro-controller. For large runs, these parts look pretty competitive.

    I wonder if you would be sued by Maxim or Austria Microsystems “if” you could program a cheap micro-controller to be a drop-in replacement and open-sourced the code and HW design?

  6. Anka06 says:

    I agree, a good idea, but a little expensive…

  7. voidptr says:

    Interesting board :-) Maxim is expensive in low volume tho …

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