DC1070 QUICK START QUIDE
DEMO CIRCUIT DC1070
QUICK START GUIDE
P R O G R A M M A B L E G A IN ,
IN S T R U M E N TA T IO N A M P L IF IE R , L T C 6 9 1 5
DESCRIPTION
A DC1070 demonstration circuit features the LTC6915
I a programmabl gain instrumentation ampl
C,
e
ifier.
The LTC® 6915 is a precision programmabl gain in-
e
strumentation ampl
ifier. The gain can be programmed
to 0, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048,
or 4096 through a paralel or serialinterface. The offset
l
ow
ess
is bel 10 V with a temperature drift of l than
50nV/ The LTC6915 uses charge bal
°C.
anced sampl
ed
data techniques to convert a differential input vol
tage
into a singl ended signal that is in turn ampl
e
ified by a
zero-drift operational ampl
ifier. The LTC6915 can be
used in singl power suppl appl
e
y
ications as l as
ow
2.7V,or with dual±5V suppl
ies.
The DC1070 contains an LTC6915, an LCD displ and
ay
switches and a PI (micro-controler). The PI reads
C
l
C
the settings of the switches, sends a paralel or a serial
l
controlword to the LTC6915 and displ the PGA gain
ays
on the LCD displ The LTC6915 on the DC1070 can
ay.
be controled with an external paralel or serial digital
l
l
control by moving wire j
umpers A-F from position 1-2
to 2-3 and connecting six external digital control l
ines
to on board turrets.
Fi
gure1. LTC6915 Bl Di
ock agram
1
DC1070 QUICK START QUIDE
Qui TestProcedure:
ck
1. Turn on power suppl The green LED over SW 6 shoul be on.
y.
d
2. Press the UP push button SW (SW 11) repeatedl and the LCD displ shoul step thru AV:1 to Av:4096 in
y
ay
d
powers of two (1,2,4,8,16,32,64,128,512,1024,2048,and 4096).
Press the DOW N push button SW (SW 12) until Av: 1. Press the SEND push button SW (SW 13) and then the
STORE push button SW (SW 14). Channel 2 shoul show a 1Vp-p, 50Hz, sinewave (
the STORE push button
d
SW saves a PGA gain setting so that it is the gain setting when the board is powered-up).
Press the M I GAI
N
N
push button SW (SW 9) and the LCD displ shoul fl “M I GAI SET”.
ay
d ash
N
N
3. Press the UP push button SW untilAV:4. Press the M AX GAI push button SW (SW 10) and the LCD displ
N
ay
shoul fl “M AX GAI SET”.
d ash
N
4. Press and hol the STEP UP push button SW (SW 7) for about three seconds and channel2 shoul show a
d
d
4Vp-p,50Hz,sinewave (M AX GAI setting).
N
5. Press and hol the STEP DOW N push button SW (SW 8) for about three seconds and channel2 shoul show a
d
d
N
N
1Vp-p,50Hz,sinewave (M I GAI setting).
d
6. Set SW 5 up (HOLD). The green LED over SW 5 shoul be on and the gain setting can not be changed with any
other switch (SW 7-14).
7. Set SW 5 down (THRU).
AL). Steps 2-8 can be repeated in SerialM ode.
8. Set SW 6 down (SERI
Note:
the LTC6915 -3dB bandwidth is approximatel 400Hz
.
y
________________________________________________________________________________________
U si a Bri Sensor w i h a D C1070
ng
dge
t
Figure 3 shows the DC1070 connections using a bridge sensor as an input signalsource. The bridge sensor can
be any sensor that is configured as a W heatstone resitive bridge with one two or four sensor el
ements. Figure 4
shows a resistive bridge that can be used to simul the output of a W heatstone bridge sensor.
ate
TestProcedure U si t Fi
ng he gure 4 Bri
dge
1. O n DC1070 set SW 3 to CO M and SW 15 to EXT and Connect Figure 4 bridge to DC1070 as per Figure 3.
2. Connect bridge suppl DC1070 power suppl vol
y,
y, tage source and 6 1/ DM M as per Figure 3.
2
3. Set the bridge suppl and the DC1070 power suppl to 3.0V and the vol
y
y
tage source connected to EXT
VR EF to 1.5V. N ote:The externalreference vol
tage sets the output DC reference (VR EF). The bridge input
is equal to [PG A O U T-VR EF]/ A G AI ). I a singl suppl operation, if the bridge input is positive
(PG
N n
e
y
(I +>I -) then VR EF can be 0V. I the bridge input is ±Vol then VREF shoul be at l
N N
f
ts
d
east equal to the
maximum bridge input times the PGA gain. For exampl if the maximum bridge input is ±10mV and the PGA
e
gain is set to 128 then VREF shoul
≥
128 X 10mV or 1.28V. W ith a 3V LTC6915 and a VREF equal to 1.5V,
d
the maximum [PGA OUT-VREF] range is ±1.5V (Rl
oad≥10k).
4. Set the PGA gain to 1 using the UP and DOW N push button SW and adj the bridge 100 ohm potentiometer
ust
until[PGA OUT-VREF]=10mV.
5. M easure the bridge vol
tage [VB+OUT - VB-OUT] (this is the vol
tage of the bridge suppl The ratio of [PGA
y).
OUT-VREF]/ [VB+OUT - VB-OUT] is a measure of the bridge unbal
ance or sensor sensitivity. For exampl if
e,
the bridge sensor is measuring weight in l and for each l [PGA OUT-VREF]=10mV then [PGA OUT-VREF]/
bs
b
[VB+OUT - VB-OUT]=0.003333 and the sensor output is 0.003333/b. The ratiometric bridge measurement
l
provides for bridge sensor cal
ibration in units of a physicalvariabl (weight, pressure, temperature, ) and is
e
…
insensitive to the absol val of the bridge vol
ute ue
tage or resistance (if the bridge vol
tage and resistance is sta-
bl during a measurement).
e
3
DC1070 QUICK START QUIDE
Fi
gure 5. TestSet Usi Ext
up ng ernalDi t Cont and M easurem ent
gial
rol
U si a D C1070 w i h Ext
ng
t
ernalCont and M easurem ent
rol
Figure 5 shows the DC1070 connections for external digital control and measurement. The digital control l
ines
can be serialor paralel(the LTC6915 data sheet defines the digitalcontroll functions and vol
l
ine
tage l s).
evel
TestSet f Ext
up or ernalCont and M easurem ant
rol
1. The DC1070 is provided with wire j
umpers A-F in position 1-2 and for externalcontrolthe wire j
umpers
must be in position 2-3.
2. Set SW 4 on DC1070 to D-O FF (the power to the DC1070 PI and LCD displ is disconected).
C
ay
3. Connect a bridge sensor,suppl externalvol
ies,
tage source and ratiometric ADC as shown in Figure 5.
4. U sing the Figure 5 setup and the the test procedure for Figure 3 setup as a guide, a compl system of
ete
digitalcontroland measurement for a bridge sensor can be eval
uated.
5
Embedded System
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