Connector CN1
Pin
Name
Function
1
IN HI
Positive measuring input
2
IN LO
Negative measuring input
3
VDD
Module DC positive 5V or +9V
4
VSS
Module DC negative supply 0V
5
COMMON
Analog common input
6
BL+
Backlight: connect to +5V or with external resistor for +9V supply *
7
REF LO
Negative reference voltage input
8
REF HI
Positive reference voltage input
9
BP (Selected)
Connect to annunciator or decimal point inputs
10
BP (Not Selected)
Connect to all unused annunciator or decimal point inputs
11
BL-
Backlight negative supply. Note: connect directly to OV not to pin 4
12
DP3
Decimal point 1.999
13
DP2
Decimal point 19.99
14
DP1
Decimal point 199.9
Links and Mode Connections (page 12)
Function
HED281/DPM951
HED282/DPM952
Links ANALOGUE COMMON to IN LO
Connect CN1 pins
2-5
Solder LK1
Links ANALOGUE COMMON to VSS
Connect CN1 pins
4-5
Solder LK2
Links REF LO to ANALOGUE COMMON
Connect CN1 pins
7-5
Solder LK3
Links REF HI to VR1 (remove link if using external reference voltage
circuit)
Solder LK4
Solder LK4
Power supply voltage mode link (see Power Supply Selection)
Solder LK5
Solder LK5
Power supply voltage mode link (see Power Supply Selection)
Solder LK6
Solder LK6
TEST LINK. Forces display to 1888. Do not use for more than 2
seconds or damage to the display may occur
Briefly bridge LKT
Briefly bridge LKT
Analogue Inputs
IN HI, IN LO and REF HI are all differential inputs. They respond to the voltage across them and not to the
voltage with respect to the power supply. The only exception to this is in 5V mode where the analogue
common and VSS have been connected together. There is a limit to the voltage which can be measured
using a differential input and this is known as the common mode range. No input may be taken outside the
range VDD minus 0.5V and VSS plus 1.0v. If there is a danger that any input may be taken outside these
limits, it is necessary to fit a resistor of suitable value to limit the current to 100µA in series with the input or
damage to the unit may occur.
Connector CN2 (HED282/DPM952 only)
Pin
Annunciator
Function
1
BP (Annunciator Not Selected)
2
A
Amps
3
°C
Degrees Celsius
4
°F
Degrees Fahrenheit
5
µ
Micro
6
m
Milli
7
K
Kilo
8
M
Mega
9
Ω
Ohms
10
V
Volts
11
BP (Annunciator Selected)
Annunciators (page 12)
To display an annunciator, solder a
connection between the required
Annunciator solder pad and the
adjacent BP (Selected) solder pad. For
the annunciators that are not in use,
solder a connection between the
associated Annunciator solder pad and
the adjacent BP (Not Selected) solder
pad to ensure that they do not appear.
3
* 281/951: 68
Ω
282/952: 33
Ω
