Topics

TIL311 LED display current draw #ELF #History #Electronics


Ham Radio
 

The TIL311 LED  hex displays used by the ELF were introduced by TI in 1972.  

Even by today’s standards, having a hex display with a 4 bit latch in a single 14 pin DIP package is impressive.
The catch — these displays take quite a bit of current  to light all those LEDS!

Below is a table with each digit lit and the current drawn with VCC at about 4.97 volts.
0.  122 ma
1.  111 ma
3.  120 ma
4.  122 ma
5.  128 ma
6.  119 ma
7.  120 ma
8.  116 ma
9.  120 ma 
A.  132 ma
B.  133 ma 
C.  122 ma.
D.  134 ma.
E.  133 ma.
F.   127 ma.


If you want to reduce the current used by the TIL311s,   a 50 ohm resistor in the VCC line of the TIL311 reduces the current draw by about  33% (at the cost of having the display be about half brilliance).  If you are running your ELF on battery power, you may want to consider the current limiting resistor.

My whole 1802 SBC board only consumes 37 ma!

The 5 TIL311s  that were used for my tests were made in Korea and have a date code of 0346.  They look new.
--
Regards,
Bernie Murphy


Ham Radio
 
Edited

Note that the table provided was the total current draw of the 1802 system.  Subtract 37 ma to get the actual TIL 311 current draw.
--
Regards,
Bernie Murphy


Steve Gemeny
 

For situations focused on low power I had always thought an LCD display might be nice...
I had considered (but never implemented) a few different approaches...
— displaying  the data and low address In the top (address) and bottom (data) eight segments (as on not) of a 4 character 7-segment LCD display...
—decoding the addresses and data into individual 2 digit 7-segment LCD displays.

I’m sure there are other approaches that could be made to work, I just never found any round-Toits 

Steve


Sent by my fat thumbs drifting aimlessly  across tiny soft I Keys...

On Sep 1, 2020, at 2:00 PM, Ham Radio <bernard.murphy@...> wrote:



The TIL311 LED  hex displays used by the ELF were introduced by TI in 1972.  

Even by today’s standards, having a hex display with a 4 bit latch in a single 14 pin DIP package is impressive.
The catch — these displays take quite a bit of current  to light all those LEDS!

Below is a table with each digit lit and the current drawn with VCC at about 4.97 volts.
0.  122 ma
1.  111 ma
3.  120 ma
4.  122 ma
5.  128 ma
6.  119 ma
7.  120 ma
8.  116 ma
9.  120 ma 
A.  132 ma
B.  133 ma 
C.  122 ma.
D.  134 ma.
E.  133 ma.
F.   127 ma.


If you want to reduce the current used by the TIL311s,   a 50 ohm resistor in the VCC line of the TIL311 reduces the current draw by about  33% (at the cost of having the display be about half brilliance).  If you are running your ELF on battery power, you may want to consider the current limiting resistor.

My whole 1802 SBC board only consumes 37 ma!

The 5 TIL311s  that were used for my tests were made in Korea and have a date code of 0346.  They look new.
--
Regards,
Bernie Murphy


Lee Hart
 

Steve Gemeny wrote:
For situations focused on low power I had always thought an LCD
display might be nice... I had considered (but never implemented) a
few different approaches... displaying the data and low address In
the top (address) and bottom (data) eight segments (as on not) of a 4
character 7-segment LCD display... —decoding the addresses and data
into individual 2 digit 7-segment LCD displays.
Way back when I started working on my Membership Card, I did a number of possible designs. One of them had an LCD used this way. I even bought some non-multiplexed 4-digit displays to experiment with.

I used the top-left and top-right segments of the four digits to display 8 vertical lines for the low-byte address, and the bottom-left and bottom-right segments for the 8 data bits. Four quad 2-in XOR gates drove the segments.

It worked, but looked like a "broken" display and took 4 chips.

I may still do it, though. One of (too many) is to build an Elf that runs on light. It will only display the 8 data bits, so each would display "1" or " ". I doscovered that the old windowed EPROMs also generate electricity (about 0.4v at a few microamps in room light). So I have 8 EPROMs for the "data" and 4 for the "mode" switches, all wired in series to provide about 5v at 3uA. The EPROMs I used have a metal ring around the window; so the plan is to use these to make touch switches to operate the Elf. :-)

Lee
--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
-- Antoine de Saint Exupery
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com