ANDERS ELECTRONICS OEM33 Service Manual

digital panel modules user guide

OEM33 3.5 digit LCD digital voltmeter

features

3.5 Digit 10mm character height LCD

200mV Full Scale sensitivity
Automatic zeroing and polarity indication
11 selectable annunciators
Easy to use decimal point selection
Built in snap fastener
Display hold feature standard

DESCRIPTION

The OEM33 is one of the world's smallest digital
voltmeters. It is an ideal replacement for analogue meters
with advantages of accuracy, size and easy mounting.
The module includes an A/D converter, LCD display of
10mm character height, and plastic housing with standard
dual in line pin terminals for easy insertion into sockets or
PC Board.

DIMENSIONS mm

Panel cut out 40.5 x 22.5
Fastening clips accept panel thickness 0.9 to 3.2mm

OPERATING SPECIFICATION

O

Operating temperature 0 to 50

Storage temperature -20 to 70

C

O

C

Operating relative humidity 80%

DISPLAY HOLD FACILITY

The OEM33 has a built in digital display hold facility. For
normal, continuous operation connect the 'Hold 1' pin to
the GD pin. To hold the present reading, connect 'Hold 1'
to VDD. Do not leave this pin floating or it will drift in and
out of hold mode.

ELECTRICAL CHARACTERISTICS TA=25OC¡

CHARACTERISTIC CONDITION MIN TYP MAX UNITS

Supply voltage (VDD) 9 Volts

Supply Current (IDD) 9 Volts

Full scale 199.9 mV

Input Impedance 100 M

Reference Voltage 9 Volts 100 mV

Overload voltage 20 V

Zero I/P Reading 0 +

Accuracy
at FSD

Linearity

Resolution 100 µV

CMRR 70 dB

Temp Coefficient 100 150 ppm/

5 Volts

5 Volts

9 Volts
5 Volts

9 Volts
5 Volts

7

4.5

9

10

5

6

500 900

+
+

+
+

5

+

2
2

+

+

1
1

+

V
V

µA

mA

1 Counts

Counts

4
4

Counts

Counts

2
2

Counts

PIN FUNCTIONS

VDD Positive supply terminal

VSS Negative supply terminal for 9 volts operation

GD Negative supply terminal for 5 volts operation

IH Input high terminal

IL Input low terminal

RH Reference high input terminal

RL Reference low input terminal

HOLD1 Connect to VDD for hold and GD for continuous

C Analogue Common

XBP For driving annunciator

BP LCD back plane

D1, D2, D3 Decimal point pins . D1 = .000, D2 = 0.00 D3 = 00.0

o

BAT,

C, oF,~,
m, µ, MΩ, KΩ,
V, A, HOLD2

The decimal point will appear if the corresponding
terminal is connected to XBP.

Annunciators

Ω

o

C

ORDERING INFORMATION

OEM33 3.5 digit, 200mV LCD Voltmeter

Revision - 14 27/08/04

All annunciators not in use must be connected to the BP
pin for suppression purposes. To light up an annunciator,
connect the corresponding pin to XBP.

USER INSTRUCTIONS

The OEM33 is designed for 5/9V supply. Incorrect supply
polarity will destroy the module immediately. It is ready
for general use when connected as in fig. 1 for 5V. For 9V
supply the module may need calibrating before use as
follows. Connect as in fig. 2, apply 100mV to the inputs
from a calibrated source and adjust VR1 until the display
reads 1000.The input range is 0-199.9mV.Over-range is
indicated by displaying a "1" in the most significant digit. If
the input voltage is reversed, a minus sign is displayed
automatically.
The module has 3 decimal points. D1, D2, D3 and 11
selectable annnunciators.
For 5V operation, IL must be connected to GD for
non-floating inputs (fig. 1) and to analogue common pin C
for floating inputs. In both cases J1 should be closed).

APPLICATION CIRCUITS

CONNECTION DIAGRAM BASIC CONFIGURATION

For 9V operation it is recommended to power from a 9V
battery. The inputs are intended to float with respect to the
supply but if they do not float they must be no closer than

1.5V from either VDD or VSS (VDD-1.5V and VSS+1.5V)
see the circuits for non-floating inputs below.

DC VOLTAGE MEASUREMENT

The input impedance becomes R1+R2. Choose accurate stable
resistors. Typically, R1=1MΩ. 9MΩ is a practical upper limit.

To measure voltages greater than 200mV
an attenuator is required. First choose R1.

R1

R2= x

EXAMPLES

IN Display VD R1 R2

V

2V 1.999V 199.9mV

10V 1500rpm 150mV

(Vin/Vd)-1

VD max. is 199.99mV

1MΩ 110KΩ

1MΩ 15KΩ

DC CURRENT MEASUREMENT

Vs

2

1Ω

0.1Ω

Ω

I

IN

S

P

0.04W

0.4W

Shunt resistance RS =

It is important to note the power
dissipation in the shunt and choose
resistor rating accordingly

P

EXAMPLES

2

Vs

S=

= IIN RS Ω

I

IN

Current R

200mV

2A

DC VOLTAGE OFFSET

To achieve a zero display reading
for a non-zero voltage input,
apply the offset voltage between
C and IL.
For a positive offset apply a
Positive signal to IL w.r.t. C.
Apply the input signal between
IH and C
Note jumper J1 must be open

NON FLOATING INPUTS (a)

Where a single 5V supply is not
suitable but you must connect your
input signal ground to the module
supply ground then either of the two
non-floating input circuits can be used.
Note that the module is set in 9V
supply mode BUT jumper J1 is left
open.

DC MULTI-RANGE VOLTAGE MEASUREMENT

For multi-range, use a 2 pole,
4 way rotary switch. 1 pole for
range select and the other to
connect the appropriate
decimal point to XBP.

DC MULTI-RANGE CURRENT MEASUREMENT

For multi-range, use, a 2 pole,
5 way rotary switch. 1 pole for
range select and the other to
connect the appropriate
decimal point to XBP

S

DC VOLTAGE RATIO MEASUREMENT

To determine the ratio between two
voltages apply the inputs as shown.

V2

=

Displayed reading

Over range occurs when

Note Jumper J1 must be closed and
the track connecting RL to C must be
cut

X 1000

V1

V2

> 2

V1

NON FLOATING INPUTS (b)

Using the formulae choose resistors to
ensure the analogue inputs are no
closer than 1.5V from either VDD or
VSS (VDD-1.5V or VSS+1.5V)

Revision - 14 27/08/04

anders

electronics plc Bayham Place, London NW1 OEU UK

Tel: [phone] Fax: [phone] www.anders.co.uk