DC to DC Converter
A Simple -5VDC OR -5 / -10 VDC, DC TO DC Power Converter
If you need minus five volts (-5VDC) for the LCD display contrast control voltage and the power supply does not have -5VDC output, a simple circuit using a ICL-7660 chip is the solution to the problem.  (See figure1)Another simple circuit using an ICL-7661 IC can be used to provide -5VDC or -10VDC to the LCD contrast control voltage circuit.  The circuit in “figure 2″ can be preset to -5VDC output, to -10VDC output, or can be switchable. The ICL-7660 is the “C-MOS” version of the popular 555 chip and ICL-7661 is the “C-MOS” version of the dual ICL-7660.
Fig. 1
Fig. 2

Solutions to Interface Problems
During the design and development of new product, hardware or software problems between the host processor and the display module sometimes occur.  These problems are usually the result of design error or an improper understanding of the host microprocessor or display module application rules.  When these problems occur, especially when the display remains blank, the immediate conclusion is often, “I must have received a bad display.”  Experience has shown that the display will not be the problem.  As an aid to the designer, a step-by-step trouble-shooting procedure follows which will help pin-point the cause of most troubles.Step 1: Power Supply
Refer to the “Power Supply Schematics” in the next section.
Remove the questionable module from the system. On the test bench, hook up the three power supply leads EXACTLY as shown in the appropriate schematic. The proper fluid MUST be matched to the proper schematic. Use a 20K pot for a VR. Rotating the pot iin one direction will produce a blank display. Rotating the pot in the opposite direction will produce a display with all pixels “ON” in the top character line or in the case of four-line displays, all pixels in the first and third character lines will be “ON”. This shows the display to be functioning properly. Now rotate the pot so the pixel pattern is barely visible.

DISCUSSION: Display modules require two voltages to function properly. Both schematics require +5VDC across VDD and VSS. This voltage powers the ICs on the module. The fluid bias voltage is across VDD and VO and is derived from the pot VR. The fluid bias voltage can be adjusted from 0 to +10V in the schematic to the right and from 0 to +5V in the schematic to the left.

Step 2:  Initialization
Refer to the “Initialization or Reset” information in the previous Section.
Hookup the remaining I/O lines to the  display module.  Make sure the pixel pattern is barely visible.  Send the appropriate HEX codes to initialize the display.  For a two-line display, send HEX 38,38,06,0E,01.  Remember, as each HEX code is put on the data bus, the enable line must be strobe.  The duration of the enable strobe pulse must be 450ns minimum.  Information on the data bus will be transferred to the display instruction register on the falling edge of the strobe pulse.  Once all HEX codes of the initialization procedure are strobed into the display instruction register a steady state cursor will appear at the first character position of the top line.  If the cursor appears, the display has been initialized.  If no cursor appears, transfer of data is nottaking place and there is most likely a problem with the enable strobe pulse timing. Refer to “Timing Characteristics” below.DISCUSSION:  Display modules are designed with a built-in initialization on “Power-Up.”  This built-in procedure initializes all displays as on line and with the display function off (blank).  During the developmental phase of a new product, display modules should be reinitialized via software using the HEX codes provided.  This will allow the designer to visually confirm when the display has been initialized.  Failure to initialize at this point is almost always due to timing errors (see following sections).The above procedures are valid for most Shelly displays.  Some occasional troubles and solutions are listed below. Should your display not function as described above, please consult the factory.
Symptom Possible Cause
Erratic or unreliable operation
A
a.A
b.A
Transmitting too fast to display
Bad solder joints at header
Missing or weak pixels
(usually permanent damage)
A
A
a.A
b.A
A
c.A
ESD damage
Disconnection of EL lamp terminals with inverter still “ON”
Disassembly of display module
Only the first 8 characters of a16 character display will function
A
aA
A
A
This display has only one IC, and must be initialized as though it is a two-line display.

Timing Characteristics
Write Operation
Read Operation
Note:  Rs line must be on 140 µs or more before the E line goes high.


Power Supply Requirements
+ 5 VDC
Fig. 3
+ 5 VDC  &  - 5 VDC
Fig. 4
VR 10K – 20K
Module
Type
Fluid
Type
Power Supply Voltage Input
TN S Fig. 3  + 5VDC
TN H Fig. 4  + 5VDC & – 5VDC
TN W Fig. 4  + 5VDC & – 5VDC
STN H Fig. 3  + 5VDC
STN M Fig. 4  + 5VDC & – 5VDC
STN T Fig. 4  + 5VDC & – 5VDC