Help for an unknown 4-digit, 7-segments LCD

Hi all, I have discovered a 4 digit, 7 segments LCD (40 pin dip). I bought it about 30 years ago but it never use it. Now I have a little project in my mind and I think to use it with its driver (Maxim ICM7211).

Looking in the net I have found a picture of a LCD that seems very similar to mine (BZTN120701-11) but I have no idea about the electrical connection nor I found any datasheet.

Can anyone suggest me any idea?

Thank you in advance and have a nice week.

Lorenzo

Can anyone suggest me any idea?

Post some picture of the thing?

robtillaart: Post some picture of the thing?

I haven't, but is very similar to this one (http://www.alibaba.com/product-detail/Transparent-Segments-Icon-LCD-Display_1003262315.html)

Sorry - brings no further clue :(

with the Liquid-Crystal Display (LCD) Tester

http://www.eeweb.com/blog/extreme_circuits/liquid-crystal-display-lcd-tester

the pin BP (backplane) is most often the first top left

elektrax: with the Liquid-Crystal Display (LCD) Tester

http://www.eeweb.com/blog/extreme_circuits/liquid-crystal-display-lcd-tester

the pin BP (backplane) is most often the first top left

Thank you very much. I try this solution.

Thank you elektrax for your suggestion, it works! Now I have another issue. The 7211 is a BCD-to-7segment LCD driver but it can display only numbers and letters from A to F. The display, however, has also three dots and the colon, so I can't drive them with this chip, while my idea was to build a generic lcd display to be used as a counter, a clock or something else.

I think to drive them building a circuit that use the backplane as an input to be inverted, this in order to use the same values of the other segments but I have no idea on how to do so. Maybe a transistor circuit can solve the problem?

No, [u]not[/u] a transistor. For individual segments, you drive them with an EX-OR gate (74HC86) with one input connected to the backplane.

Paul__B: No, [u]not[/u] a transistor. For individual segments, you drive them with an EX-OR gate (74HC86) with one input connected to the backplane.

Thank you Paul, but I'm not sure because, if I don't wrong, the square wave applied on segment must have negative voltage value respect to backplane to switch on the segment, in order to have 0V mean level.

{OK, the forum server did get me that time and wiped my answer.}

If the second input to the EX-OR is a zero, then the output is the same as the backplane voltage and the segment does not light. If the second input is a "one", then the output of the EX-OR is the opposite of the square wave on the backplane, and the segment lights but because the backplane has a 50% duty cycle, there is no DC offset between the backplane and its complement.

The EX-OR gate must be supplied with the same voltage as the backplane driver; if that is 5V, then the 74HC86 is appropriate, otherwise you need to use a MC14070 instead which can operate up to 18V (but requires a matching input voltage).

It should be obvious that the output stages of the ICM7211 are of course, all EX-OR gates.

Paul__B: If the second input to the EX-OR is a zero, then the output is the same as the backplane voltage and the segment does not light. If the second input is a "one", then the output of the EX-OR is the opposite of the square wave on the backplane, and the segment lights but because the backplane has a 50% duty cycle, there is no DC offset between the backplane and its complement.

I made a mistake, excuse me. I will try this solution. Thank you!