DDS Signal generator and Frequency Counter
A DDS (direct digital synthesis) Frequency Generator and independent Frequency Counter built with modular components.
This is an ongoing development of an earlier design idea: DDS Frequency Generator ~ 55MHz
The concept is to have two functions in one box, but with a common switchable LCD display being used for both.
Materials:
A DDS generator, and frequency counter are housed in one enclosure and routed to a common switchable LCD display, through a 6 line 2 position relay board.
12 volt external DC supply is used for the relay board and also feeds;
A 7808 voltage regulator: supplies the DDS and freq counter modules.
and A 7805 voltage regulator: supplies the 1602 LCD display
4 data lines (D4 - D7) and a 2 line control bus (RS register select and E Enable)
are needed to interface/drive the 1602 LCD display - from either (ported/switched) module.
The switching (multiplexing) is acheived by 3 parallel'ed coil connected minature relays
(each relay has two sets of 'changeover' contacts i.e DPDT)
Additionally as the only minature relay's I had readily available were 24V DC coil rated:
I had to use a voltage-booster type of circuit to allow 12 V DC operation.
The 24V relay coil min-op is about 13.5V DC, therefore it will not "pick-up" at 12 volts.
Boost Circuit Operation:
The 220uF capacitor is pre-charged.
When the switch is thrown the 12V supply and capacitor voltage are connected in series aiding,
which places approx 24V across the coil.
The relay will smartly pick-up, the capacitor will discharge,
and the relay will be held-in by the 12V rail (thru a diode)
These relays should seal-in at any voltage greater than about 8V.
3 identical relays are driven with this circuit.
See also: How to drive 24V relay with 12V-Vcc http://www.intio.or.jp/jf10zl/24vr.htm
and.... Use 24 V relays at 12 V http://www.qsl.net/i0jx/relay.html
This is actually a more efficient way of using a relay than running it at its full rated voltage. Finished construction
Technical support
For anyone who would critique the use of mechanical relays as a multiplexing switch;
I initially did prototype; chip circuit designs using both TTL 74LS157 and CMOS 4053 multiplexing devices.
However because of some sort of incompatibility between the TTL/CMOS families and the module/display electronics, I couldn't get my idea to work!
Therefore low ohmic, contact relays were the only other thing I could utilise!
The DDS will still produce an O/P even when counter mode is selected.
The centre off position when switching from DDS to counter (and vice versa)
is to allow a reset of each module so as 1602 will display the correct information.
© 1Q 2018
This is an ongoing development of an earlier design idea: DDS Frequency Generator ~ 55MHz
The concept is to have two functions in one box, but with a common switchable LCD display being used for both.
Materials:
A DDS generator, and frequency counter are housed in one enclosure and routed to a common switchable LCD display, through a 6 line 2 position relay board.
12 volt external DC supply is used for the relay board and also feeds;
A 7808 voltage regulator: supplies the DDS and freq counter modules.
and A 7805 voltage regulator: supplies the 1602 LCD display
4 data lines (D4 - D7) and a 2 line control bus (RS register select and E Enable)
are needed to interface/drive the 1602 LCD display - from either (ported/switched) module.
The switching (multiplexing) is acheived by 3 parallel'ed coil connected minature relays
(each relay has two sets of 'changeover' contacts i.e DPDT)
Additionally as the only minature relay's I had readily available were 24V DC coil rated:
I had to use a voltage-booster type of circuit to allow 12 V DC operation.
The 24V relay coil min-op is about 13.5V DC, therefore it will not "pick-up" at 12 volts.
Boost Circuit Operation:
The 220uF capacitor is pre-charged.
When the switch is thrown the 12V supply and capacitor voltage are connected in series aiding,
which places approx 24V across the coil.
The relay will smartly pick-up, the capacitor will discharge,
and the relay will be held-in by the 12V rail (thru a diode)
These relays should seal-in at any voltage greater than about 8V.
3 identical relays are driven with this circuit.
See also: How to drive 24V relay with 12V-Vcc http://www.intio.or.jp/jf10zl/24vr.htm
and.... Use 24 V relays at 12 V http://www.qsl.net/i0jx/relay.html
This is actually a more efficient way of using a relay than running it at its full rated voltage. Finished construction
Technical support
For anyone who would critique the use of mechanical relays as a multiplexing switch;
I initially did prototype; chip circuit designs using both TTL 74LS157 and CMOS 4053 multiplexing devices.
However because of some sort of incompatibility between the TTL/CMOS families and the module/display electronics, I couldn't get my idea to work!
Therefore low ohmic, contact relays were the only other thing I could utilise!
The DDS will still produce an O/P even when counter mode is selected.
The centre off position when switching from DDS to counter (and vice versa)
is to allow a reset of each module so as 1602 will display the correct information.
© 1Q 2018