Data sheet for 4 digit 7 seg display with 7 pins?

[dobsonr741]

A Chinese made speaker had a strange 7 segment 4 digit clock display, with only 7 pins. Does anyone have a data sheet of a similar part? I assume a driver is inside, question is how to drive it.

[Chat GPT]

It's difficult to provide a specific data sheet without knowing the exact model or part number of the display, but it's possible that the display is a common cathode or common anode display with multiplexed digits.

In this case, there may be a driver circuit inside the display that handles the multiplexing, which means that only 7 pins are needed to control all four digits of the display. To drive the display, you would typically need to send a series of signals to the appropriate segments of each digit, in the correct order and at the correct frequency to display the desired numbers or characters.

If you have a clear photo of the pinout and any markings on the display, it may be possible to identify the specific part and locate a data sheet or technical information that can provide more guidance on how to drive it. Alternatively, you may need to experiment with different input signals to determine the correct sequence and timing to display the desired information on the display.

[wasedadoc]

I do not know how this display works but two possible ways:

1. Of the 7 pins, need 2 for power which leaves 5.  5 pins which can be HIGH or LOW allows 32 states.  There are 4 digits of 7 segments each.  That is 28.  Add 1 or 2 for the colon dots and another state for nothing lit.  So that is a total of 30 or 31.  Can be done with 5 bits.

The module would contain a 5 to 32 selector with each of the display segments and dots driven from one of the 32.  Any one of them can be illuminated at a time by inputting the appropriate 5 bit code.  Drive at high enough speed so that flicker is not apparent.  Have a counter which cycles the 5 bits through the 32 states but whenever a segment or dot is not to be lit, override the counter output and send the 5 bits which correspond to the state with no segment or dot.

2.  Consider the 5 bits as 2 and 3.  2 bits can select 1 of the 4 digits.  3 bits is 8 states which is enough to select any one or none of the 7 segments.  Two multiplexes at different speeds.  Cannot control the colon dots in this scheme.  Just wire them permanently on from the power input

[Doctorandus_P]

If he's got the clock, then put an EUR10 Logic analyser on it and sniff the communication. From that it would be easy enough to figure out how it is controlled.

But why bother at all? It's a curious thing, but once your curiosity is satisfied is there anything useful you want to do with it? I just would not bother myself and consider it just a waste of time. There are many much more interesting things to do in this Wide Weird World.

[themadhippy]

it might just be charliplexed, 7 pins will control  upto 42  segments.

[Ian.M]

+1
Don't rule out Charlieplexing.  The display above may well *NOT* have an internal driver IC.

The presence of current limiting resistors between *all* the display pins and the MCU I/O pins driving them is a strong indication of a charlieplexed display.  However extremely low cost ('Muntzed') designs may omit them, relying on the output resistance of the I/O pins to limit the LED current.

If the original board is still available and can be powered up, investigation with a scope, and then a logic analyser is called for.

If not, manually tabulating the display's 'signature' (i.e. checking if there is a diode or resistance between every possible pair of pins, and if its a diode, measuring the Vf), should determine whether or not a driver chip is present, and if present, distinguish between its control and power pins.  If single segments illuminate during this test, its charlieplexed, and if you note their locations, you are well on the way towards mapping it for reuse.

[coromonadalix]

based only with led :  the classic approach is put a dmm into diode test  and try many combinations  until you see led lightning

write your findings on a sheet and do your own display table

[Ian.M]

Yep, start with a 7 row by 7 column grid, with both rows and columns numbered with the pin number, with the leading diagonal (where row=column) struck out. Clip the negative lead of the tester onto the pin for that row, and probe each remaining pin in turn with the positive lead.  For each cell in the row, note the digit position and segment letter or - if nothing illuminates.   There are only 42 possible combinations so you should be done in ten minutes if you work methodically!

[dobsonr741]

Charlieplexed, indeed. Very well explained on https://electronics.stackexchange.com/questions/321602/where-can-i-find-a-datasheet-info-of-on-this-music-speakers-35-segment-led-dis

Quick test with a current limited source revealed no driver but direct connected LEDs are inside. 7 pin more than enough to drive 7x4+1 in Charlieplexing, even 6 pins are sufficient. Seems though all 7 are used.

 

[retiredfeline]

Another possibility is internal shift registers.