I have a product where I have two three-digit 7-segment displays driven by a MAX7219. Works great but I'm always on the lookout for improvements.
One of those improvements is using the bezels from Chinese voltmeters you can get on ebay for less than a couple bucks. The link describes my idea in detail, but basically, I want to remove the voltmeter electronics and display and replace it with 3 digits and a MAX7219 driver. That seems like a handy thing in general and maybe a nice way of having the two readouts I have now.
In the current scheme, digits 0-2 are one display, and 3-5 are the other display. The MAX chip uses a shift register type interface with addressable registers for each each digit.
Thereason are two usual ways of cascading MAX7219s. The chips can be connected in series, with the Dout pin of the first feeding the Din pin of the second, and extra bytes are inserted to shift the data to the right chip. Alternately, the data lines (data, clock and latch) may be connected in parallel, and which chip receives the message is controlled by the enable lines.
In my drug-adled state (2 weeks post knee replacement surgery), I think I have a better way of handling this, which requires no changes in firmware. If I connect the digits in display 1 to the MAX D0-D2 lines, and the digits in display 2 to the MAX D3 -D5 lines and I connect the data lines in parallel, both displays get all of the messages but each MAX only displays what it should...well, each is trying to display all 6 digits, but only 3 have LEDs connected and matter.
Am I missing anything here?
One of those improvements is using the bezels from Chinese voltmeters you can get on ebay for less than a couple bucks. The link describes my idea in detail, but basically, I want to remove the voltmeter electronics and display and replace it with 3 digits and a MAX7219 driver. That seems like a handy thing in general and maybe a nice way of having the two readouts I have now.
In the current scheme, digits 0-2 are one display, and 3-5 are the other display. The MAX chip uses a shift register type interface with addressable registers for each each digit.
Thereason are two usual ways of cascading MAX7219s. The chips can be connected in series, with the Dout pin of the first feeding the Din pin of the second, and extra bytes are inserted to shift the data to the right chip. Alternately, the data lines (data, clock and latch) may be connected in parallel, and which chip receives the message is controlled by the enable lines.
In my drug-adled state (2 weeks post knee replacement surgery), I think I have a better way of handling this, which requires no changes in firmware. If I connect the digits in display 1 to the MAX D0-D2 lines, and the digits in display 2 to the MAX D3 -D5 lines and I connect the data lines in parallel, both displays get all of the messages but each MAX only displays what it should...well, each is trying to display all 6 digits, but only 3 have LEDs connected and matter.
Am I missing anything here?