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LED display LED displays used in HP calculators

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The first series of the Hewlett Packard pocket calculators used a LED (Light Emitting Diode) display. The development of LED displays enabled to build small, reliable pocket calculators that could be supplied by batteries. The LED display consumes a significant amount of power (compared to LCD), which results in a short battery life span. To avoid the regular exchange of batteries, the calculators were supplied by rechargeable batteries. These batteries can be charged inside the calculator by means of a charger. A benefit of the LED display above the LCD is the fact that LED display are active displays, light is emitted. This improves the readability in bad illuminated environment.

 

The Classic series

Display Classic

The picture above shows the 15 digit LED display from a Classic series calculator. The 15 digits are composed of 3 modules of 5 digits each. The two chip above the LED displays are the LED segment drivers (1858-0050-1D) and the LED digit drivers (1820-1749).

Click here to download a pdf file with a data sheet of this type of LED displays.

Each digit contains 7 LED segments and a dot. This can be observed in the next picture.

Digit Digit

Each segment is divided in three bars. The point is composed of two bars. This picture also shows the golden wires that connect the segments with the preceding digit and with the next digit. Many thanks to R. Backus for sharing these nice pictures.

 

Display HP55C

The picture on the left shows the readout of this display. The division is fixed. The first digit is used only for the minus sign. The next 11 digits are used to display the mantissa and the decimal separator. This decimal separator occupies a complete digit. The 13th digit displays the sign of the exponent and the last two digits display the exponent itself. The decimal separator is placed inside the 7 segment display in stead of left or right of the digit. This placement is patented by Hewlett Packard. This patent can be downloaded here as a pdf file. More information about the display of the Classic series can be found here.

 

The Topcat series

The Topcat series are desktop calculators. This series have a larger size LED display to improve the readability.

Display Topcat

The number of digits and the division is equal to the display of Classic series.

I don't have a picture of the display module because this module can not easy be disassembled. It is melted to the red plastic cover. The next picture shows the backside of this module. The three red heat stakes are clearly visible.

Display HP97

 

The Woodstock series

For the second series LED display calculators, the Woodstock series, one module with a 12 digit display is used. The readout of this woodstock display is shown in the picture below.

Display Woodstock

So far two different LED modules were found, labeled: 1990-0495 and 1990-0559. Both look identical. These modules count 20 pins. The digit segments are organized in a common cathode matrix. Eight connections are used to select the 7 digit segment and the decimal separator. The other 12 connections are used to select the digit.

Display Woodstock HP22 display back

The pinning of this 1990-0495 display is shown in the next table.

Hole
Function
Hole
Function
1
segment A
11
digit 9
2
segment F
12
digit 12 (Most left digit)
3
segment B
13
digit 8
4
segment C
14
digit 1 (Most right digit)
5
segment D
15
digit 7
6
segment Dp
16
digit 2
7
segment E
17
digit 6
8
segment G
18
digit 3
9
digit 10
19
digit 4
10
digit 11
20
digit 5

 

The Sting series

The Sting models uses a 12 digit LED display. It seems simular as the display of the Woodstock series, except for the decimal separator. This separator occupies a complete digit as in the Classic series. The figure below shows the display of the HP-10.

HP10 Display HP10_display_back

This display counts 13 lens bubbles but only 12 of them cover a digit. The right most position is empty.
The display is labeled 1130-0536, printed on the back. Measurements result in the following pinning.
The holes are numbered from the left to the right.

Hole
Function
Hole
Function
1
segment A
12
digit 13 (Most left digit)
2
segment F
13
digit 9
3
segment B
14
digit 2
4
segment C
15
digit 8
5
segment D
16
digit 3
6
segment Dp
17
digit 7
7
segment E
18
digit 4
8
segment G
19
digit 5
9
digit 11
20
digit 6
10
digit 12
21
digit 1 (Most right digit, not assembled)
11
digit 10    

 

The Spice series

The display of the Spice series readout as shown in the picture below.

Display Spice Series

The Spice series have a LED module of 11 digits.
The first digit contains only a minus sign, the other 10 digits are normal 7 segment displays. The decimal separator is build from two small segments. The upper part is a point, the lower part is a comma.

Display Spice Series

The table below shows the pinning of this display, labeled1990-0567.

Pin
Function
Pin
Function
1
digit - (most left digit)
12
digit 5
2
anode - (minus sign)
13
digit 4
3
segment point
14
digit 3
4
segment C
15
digit 2
5
segment comma
16
digit 1 (Most right digit)
6
segment E
17
segment D
7
digit 10
18
segment G
8
digit 9
19
segment F
9
digit 8
20
segment A
10
digit 7
21
segment B
11
digit 6
22
digit - (minus sign)

 

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HP LED display related links:

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