Remote switching circuit utilizes voltage logic to switch on desired circuit. Circuit controls rotating multi-range pressure transducers in jet engine testing and can be used in coded remote circuit activator where sequence of switching has to occur in defined length of time to prevent false or undesired circuit activation

Peterson, V. S.

English

NASA Technical Reports Server

4 
October 1970	 Brief 70-10579 
NASA TECH BRIEF 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Solid State Remote Circuit Selector Switch
To Additional 
Switch Circuits 
as Required 
4 Remote Switch Circuits 
4 Local Control Circuit
+ Control 
Power Supply 
To Additional 
Control Circuit 
Ganged Switch I	 as Required 
Sections
Current Shows Which 
JLoad is on 
+ Load Power Supply 
Power Corn 
A solid-state remote switching circuit has been 
developed that differs from existing circuits in that 
voltage logic is used to switch on a desired circuit. 
Mechanical relays, frequency responsive circuits, or 
capacitors in the remote load switching circuit are 
not required. The switch circuit was orginally designed 
to control rotating multi-range pressure transducers 
in jet engine testing. In addition to the above, the 
circuit meets the following requirements: a three-
conductor wire connection between the central control
circuit and the remote switch circuits; a continuous 
central control circuit indication of the remote switch 
circuit that is activated; and a capability of activating 
any remote circuit switch in any order of desired 
sequence. 
The schematic illustration shows how the system 
functions. The remote switching action is produced 
by a silicon controlled rectifier (SCR) Q2 conducting 
current through loads 1, 2, 3, etc. The SCR's are 
latched to the on state by the application of current 
(continued overleaf) 
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to the gate terminal and are cut off by the momentary 
interruption of current through the anode and cathode 
conduction path. 
Q2 load current is routed via line 1 as a series con-
nection through one section of each of the central 
control circuit spring return control switches Kl, K2, 
K3, etc., and returns to circuit ground via line 2. A 
second section of the control switches applies a poten-
tial to the input of amplifier (A), as determined by 
the setting of rheostat P, when any of the control 
switches are depressed. The output of amplifier (A) 
is routed through line 3 to the SCR gate "inhibit" 
or "fire" circuits. 
The SCR gate "inhibit" or "fire" action is deter-
mined by the voltage conduction values of the zener 
diodes ZD1, ZD2, ZD3, ZD4, ZD5. In switch circuit 
(1), when Kl is depressed, the dc output voltage from 
amplifier (A) is slightly below the conduction value of 
ZD1; current will.flow through CCD and Dl, to the 
gate of Q2 and turn on the current through load 1. If 
the output voltage of amplifier (A) is above the con-
duction value of ZD1, a potential will appear at the 
base of transistor Qi, causing the transistor to conduct 
and inhibit the gate current path through ZD1 and 
CCD. If K1 is momentarily depressed under these con-
ditions, the current through line 1 will be interrupted 
for the period of time it takes the wiper of the switch 
section to leave the N.C. contact and the load 1 current 
will cease. Switch circuit (1) can be turned on only 
when the voltage on line 3 is below the conduction 
value of ZDI. Diode D9 and capacitor C provide 
hold-in current for Q2 during the short interval when 
the switch KI returns to the up position as it is re-
leased from the depressed condition. 
The Qi gate control circuit for switch circuits 2, 
3, etc., is the same as circuit (1) except for the voltage 
conduction values of the two zener diodes. In circuit 
(2), the voltage conduction value of ZD3 is selected 
to be more than that of ZD1. The voltage conduction 
value of ZD2 is higher than ZD3. When K2 is de-
pressed, and the voltage level from P1, in its circuit, 
is set so that amplifier (A) output voltage is above 
the conduction values of ZD3 but below that of ZD2, 
switch circuit (2) will turn on and switch circuit (1) 
will turn off if it was in the on state.
The zener diodes in each switch circuit set a voltage 
band that will operate the circuit. An easily set volt-
age band will fire the gate of one stage, inhibit the 
gates of preceding stages, but will not be high enough 
to fire the gates of succeeding stages. Potentiometer 
P1 is set up once to produce a voltage that falls within 
the desired band for the switch circuit selected. 
In the case where loads 1, 2, 3, etc., draw identical 
current, shunt resistors R3, R4, etc., can be selected 
to produce increasing line (1) currents for switch cir-
cuit identification as indicated by meter (M). The 
constant current diodes (CCD) limit circuit current 
drain to prevent component damage and excessive 
power supply drain. 
Notes: 
1. The multirange pressure transducer range switch-
ing requirement was a 10-circuit switching capacity. 
Larger switching capacity is possible and limited 
only by the closeness of the voltage bands and the 
voltage breakdown limitations of the constant cur-
rent diodes. The circuit can also be used in a coded 
remote circuit activator where a predetermined 
sequence of remote switching has to occur in a de-
fined length of time to prevent false or undesired 
circuit activation. 
2. Requests for,
 further information maybe directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B70-10579 
Patent status: 
This invention is owned by NASA, and a patent

application has been filed. Royalty-free, nonexclusive

licenses for its commercial use will be granted by

NASA. Inquiries concerning license rights should be

made to NASA, Code GP, Washington, D.C. 20546.

Source: V.S. Peterson
Lewis Research Center

(LEW-10387) 
Brief 70-10579	 ,	 Category 01,02


Solid state remote circuit selector switch

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