Click On Any Section of the Schematic
Below for Information on That Part of the Circuit:
AC Wiring:
AC power comes in through the line cord. The white neutral wire goes to one
side of the pilot light, and one side of the V+ power transformer, AC outlet,
and 120V control relay. The black hot wire goes through the power switch to the
other side of the V+ power transformer and one terminal of the 12V timer relay
NO contacts. When the timer circuit closes the timer relay contacts, AC is
applied to the other side of the AC outlet and control relay coil, turning both
on.
AC Wiring
Click On Any Section of the Schematic
Below for Information on That Part of the Circuit:
Operation:
AC power comes in through the line cord. The white neutral wire goes to one
side of the pilot light, and one side of the V+ power transformer, AC outlet,
and 120V control relay. The black hot wire goes through the power switch to the
other side of the V+ power transformer and one terminal of the 12V timer relay
NO contacts. When the timer closes the timer relay contacts, AC is applied to
the other side of the AC outlet and control relay coil, turning both on.
Line Cord:
The line cord should be of the grounded type. The supply draws very little
current, so just about any grounded cord can be used.
Power Switch:
The power supply draws so little power that just about any switch that can
handle 120V can be used. I used a small toggle switch with a rating of about
1A.
Pilot Light:
I used a 120V green neon pilot light that already included the correct dropping
resistor. The pilot light is on the front panel.
V+ Power Supply:
Information on the V+ power supply can be found on the
power supply page.
12V Timer Relay:
The 12V timer relay is controlled by the timer circuit. When the timer circuit
activates the relay, the contacts close and apply AC power to the control relay
and the AC outlet. The relay contacts should be able to handle 1A at 120V AC.
AC Outlet:
When the timer relay is activated, the AC outlet is turned on. Any item plugged
into the outlet, such as an antenna changeover relay, is then activated.
Current should be limited to 1A. I used an outlet that snaps into the back
panel. However, if you lack such an outlet, you can cut the end off of an
extension cord, pass it through a rubber grommet or cord strain relief in
the back panel, and use it instead of the outlet.
120V Control Relay:
When the timer relay is activated, the control relay is activated, and the
state of the various contacts on the relay is changed.
My relay was a 4PDT (4 Pole Double Throw) relay. I
only used three of the poles. I wired the normally closed (NC) contacts of one
pole to an RCA jack marked NC on the back panel. This was then wired to the
mute connection on my receiver. In receive mode, this jack is shorted to
ground, activating the receiver. When the control relay is activated, the
connection to ground is broken, and the receiver is muted.
I wired the normally open (NO) contacts of another pole to an RCA jack marked
NO on the back panel. In receive, the jack is open. When the relay is
activated, this jack is then shorted to ground, activating whatever is plugged
into it.
The normally open (NO) contacts of a third pole are used to apply AC to the
120V AC outlet. When the relay is activated, the outlet, and whatever is
plugged into it (such as an antenna changeover relay), is activated.
1N4002 Relay Surge Protective Diode:
When a relay is shut off, a voltage spike occurs that can damage the transistor
driving the relay. The diode across the relay dissipates this voltage spike.
Back to Dr. Greg Latta's
Electrical Engineering and Amateur Radio Pages
If you have any questions or
comments, you can send E-Mail to Dr. Greg Latta at
glatta@frostburg.edu