Biomedical Engineering Reference
In-Depth Information
R36
200K
+15V
+5V
-15V
C23
1uF
+
R37
20K
R38
4.99K
+5V
C24
.01uF
IC7A
TL082
4
R39
IC8
LM 311
IC9A
74 HC14
14
4 1
2
R40
-
A_PACE_IN
1
3
-
3
7
1
2
100K
+
A_PACE_DETECT
2
5.11K
+
8
C26
1uF
5 6
8
7
R41
67K
R42
100K
C25
0.1uF
+
A Pace
Detect
Threshold
3
C28
1u
F
R43
C27
.01uF
10K, trimpot
2
+
+15V
Set for 1.0
volt at the
wiper of the
trimpot.
+5V
1
C29
.01uF
+15V
+5V
R44
200K
R45
20K
R46
4.99K
+5V
IC7B
TL082
4
R47
IC10
LM 311
IC9B
74HC14
14
4 1
6
R48
-
V_PACE_IN
7
3
-
5
7
3
4
100K
+
V_PACE_DETECT
2
5.11K
+
8
R49
67K
5 6
8
7
C30
0.1uF
R50
100K
V Pace
Detect
Threshold
3
C31
1u
F
R51
10K, trimpot
2
+
Set for 1.0
volt at the
wiper of the
trimpot.
+5V
1
C32
.01uF
Figure 6.25
The atrial and ventricular pacing detector circuits sense the presence of external pacing signals delivered by a pacemaker under
test. The comparator circuits generate interrupts for the microcontroller. An
RC
network (R40 and C25 for the atrial pacing detector) ensure
that the pacing signals have sucient amplitude and duration to “capture” the simulated heart.
graph display will be on if there is enough current to forward bias each PNP transistor in
the IC, and each LED.
When enough current
flows through the internal LED of the optocoupler (IC19) to turn
the NPN transistor on, the input to IC9E is pulled to ground. This digital low is inverted
by IC9E and signals the microcontroller of a left-ventricular pacing event. Either a posi-
tive or a negative pacing signal can trigger a left-ventricular pacing event as the outputs of
the optocouplers are wire-ORed together. Figure 6.27 shows the power supply for the sim-
ulator. An external “brick” type of power supply produces
fl
15 V dc from 117 Vac. IC38
and IC39 produce
15-V power supply. Diodes D3-D10 drop approxi-
mately 0.6 V dc each and lower the input voltage to each voltage regulator. This reduces
the power dissipation by each device.
5 V dc from the
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