ANDERS ELECTRONICS OEM22, OEM24L Service Manual
digital panel modules user guide
OEM22 and OEM24L (backlit) 3.5 digit LCD digital voltmeters
features
3.5 Digit 12.7mm character height LCD
200mV full scale sensitivity
Automatic zeroing and polarity indication
Low battery indication (For 9V option only)
10 selectable annunciators
Easy to use decimal point selection
Display Hold as standard
DESCRIPTION
The OEM22 is a neat "flat pack" voltmeter module that
can either be sub-panel mounted or used with the
optional MB11 fixing bezel. The module is set up for 9 volt
operation but can be adjusted for 5V use. A low BAT
annunciator is provided as standard (9Vonly). The
OEM24L version comes complete with a green LED
backlight. All versions now come with display hold feature.
DIMENSIONS mm
OPERATING SPECIFICATION
O
Operating temperature 0 to 50
Storage temperature -20 to 70
C
O
C
Operating relative humidity 80%
ORDERING INFORMATION
OEM22 3.5 digit, 200mV LCD Voltmeter
OEM24L 3.5 digit, 200mV LCD Voltmeter with backlight
MB11 Optional mounting bezel
Revision 8 17/011/04
ELECTRICAL CHARACTERISTICS TA=25OC¡
CHARACTERISTIC CONDITION MIN TYP MAX UNITS
Supply voltage
(VDD)
Supply Current
(IDD)
Full scale 199.9 mV
Input impedance 100 M
Ref voltage ROH 9 Volts 100 mV
Overload voltage 20 Volts
Zero I/P Reading 0 +
Accuracy
at FSD
Resolution 100
CMRR 70 dB
Temp Coefficient 100 150 ppm/
Low Battery Ind. 9 Volts only 6.75 7.25 7.75 V
Backlight Volts OEM24L 5 V
Backlight Current at 5V - 40 60 mA
9 volts
5 volts
9 Volts
5 Volts
9 volts
5 volts
4.8
7
9
5
5005900
+
+
10
6
+
1
1
+
Volts
Volts
µA
mA
1 Count
Counts
2
4
Counts
µV
PIN FUNCTIONS
PIN DESCRIPTION
VDD Positive supply terminal
VSS Negative supply terminal for 9 Volt mode only
INHI
INLO
RFH
RFL
ROH
ROL
HOLD Con. to VDD for display hold, to TST for normal.
COM Analogue common
TST
XBP For driving annunciators
BP LCD back plane.
D1, D2, D3
AB,B3,E3,G3, For use with external auto-ranging circuit.
oC,o
BAT,
Ω,KΩ,V,A,HOLD
F,~,m,µ,M,
LMP + Backlight positive terminal (+5V DC) OEM24L
LMP - Backlight negative terminal ( 0V DC) OEM24L
Positive input terminal
Negative input terminal
Reference input high terminal
Reference input low terminal
Reference output high terminal
Reference output low terminal
Connect to VDD to test all segments (except
annunciators), for a few seconds only. (9V mode)
Also negative supply terminal for 5V supply.
Decimal point select. The decimal point will
energize when these pins are tied to VDD.
Annunciators. See user instructions. BAT is auto
turn on. Turn it off in 5V mode by adjusting V2.
Ω
o
C
USER INSTRUCTIONS
The OEM22/24L is designed for 9/5V supply. Incorrect
supply polarity will destroy the module immediately. It is
ready for general use when connected as in figure 1, for
9V supply. For 5V supply, the module must be calibrated
before use as follows. Connect as in figure 2, apply
100mV to the inputs, from a calibrated source and adjust
VR1 until the display reads 1000.
The input range is 0-200mV. Over-range is indicated by
blanking the three least significant digits and displaying a
"1" in the most significant digit.
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.
The low BAT voltage can be set adjusting VR2 but it is not
recommended to operate with a supply voltage below 7V.
APPLICATION CIRCUITS
DC VOLTAGE MEASUREMENT
To measure voltages greater than 200mV
an attenuator is required.
R1+R2
V
IN=VD x
EXAMPLES
IN Display VD R1 R2
V
2V 1.999V 199.9mV
10V 1500rpm 150mV
The input impedance becomes R1+R2. Choose accurate stable
resistors. Typically, R1=1MΩ. 9MΩ is a practical upper limit.
VD max. is 199.99mV
R2
1MΩ 110KΩ
1MΩ 15KΩ
CONNECTION DIAGRAM BASIC CONFIGURATION
All annunciators are connected to BP for suppression
purposes. To light up, cut the trace between the selected
annunciator pad and BP track and then link with solder
the annunciator pad to the XBP pad next to it.
For 5V operation, INLO must be connected to TST for
non-floating inputs (as fig. 2) and to the analogue common
pin COM for floating inputs. The low BAT annunciator
needs to be turned of by adjusting VR2.
MULTI-RANGE DC 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 CURRENT MEASUREMENT
DC VOLTAGE OFFSET
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 these two
non-floating input circuits can be used.
Note that the module is set in the 9V
supply mode.
Vs
2
RS Ω
1Ω
0.1Ω
.
I
IN
0.04W
0.4W
Ω
Shunt resistance RS =
It is important to note the power
dissipation in the shunt and choose
resistor rating accordingly
P
EXAMPLES
2
Vs
=
= I
S
Current RS PS
200mA
2A
To achieve a zero display reading
for a non-zero voltage input,
apply the offset voltage between
COM and INLO.
For a positive offset apply a
Positive signal to INLO w.r.t.
COM.
Apply the input signal between
INHI and COM
IN
I
IN
MULTI-RANGE DC 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.
DC VOLTAGE RATIO MEASUREMENT
To determine the ratio between two
voltages apply the inputs as shown.
Displayed reading
Over range occurs when
=
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)
V2
V1
X 1000
V2
> 2
V1
Revision 8 17/011/04
anders
Tel: +44 (0)20 7380 8167 Fax: +44 (0)20 7874 1908 http://www.anders.co.uk
electronics plc
Bayham Place, London NW1 OEU UK
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