Biomedical Engineering Reference
In-Depth Information
+12_VBAT
R94
330
IC40
8
7
6
5
Out 1-
Out 1+
Out 2-
Out 2+
D17
2
3
Anode
Cathode
1N4148
Q37
BS170
C79
10uF
C68
10uF
1
PVI1050
2
SWITCH_CHARGE
3
+5V
R95
100K
FRONT PANEL
R97
200
R98
100K
R99
100K
6
IC41A
5
3
1
IC21D
S
IC42
D
CL K
Q
MAN_CHARGE
1
8
9
8
A1
C1
SW1
2
Q
2
7
R
74HC14
K1
E1
14013
CHARGE
3
6
4
A2
C2
SW2
*SWITCH_RESET
4
5
K2
E2
DEFIB.
PS2501-2
IC41B
8
IC21E
9
11
13
S
D
CLK
Q
MAN_DEFIB
11
10
12
Q
R
74HC14
14013
10
Figure 8.45 Manual control of the defibrillation is made possible through isolated front-panel pushbuttons. A photovoltaic isolator charges
two 10-µF capacitors in parallel every 10 s through a 1-s pulse. Whenever one of the switches (SW1 or SW2) is pressed, the energy stored
in the capacitors is used to pulse the LED of the photocoupler associated with the depressed switch, starting the behavior requested (i.e.,
charge to 50 J or defibrillate).
circuit's state-machine microcontroller IC13. IC15D, IC15C, and IC15A are opened.
Almost simultaneously, IC16C connects the reference terminal of the capacitors to one of
the leads. Then the other lead is connected to C p through IC16D and dc-blocking capaci-
tor C16. The e
ff
ect of the body-lead system on a 0.1-
µ
F capacitor is sampled for 10
µ
s.
IC16D is then opened, and C a is allowed to discharge through the lead system for 10
µ
s by
way of IC16A, C16, and IC16C.
After the passive and active samples are taken, IC16C is opened to
float the lead system
in relationship to the system ground. IC16B is closed to actively discharge the dc-block-
ing capacitor for 768
fl
er-
ential signal corresponding to the compensated impedance measurement is developed by
IC14A, IC14D, and instrumentation ampli
µ
s. While active discharge takes place, IC15C is closed and the di
ff
s, the sample-
and-hold implemented through IC15B, C12, and IC14B holds the voltage level corre-
sponding to the impedance measurement. This level is then scaled and
fi
er IC17. At the end of the 768
µ
filtered through
IC14C and its associated components. Finally, the analog level is converted to a digital
fi
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