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Simple add-on board mates with the GPS Frequency Reference 1pps Driver For Quartz Clocks By JIM ROWE This simple add-on module for the GPSBased Frequency Reference is designed to drive the escapement coil of a low-cost quartz clock movement. It uses the 1Hz GPS pulses available at the rear of the Frequency Reference so that the clock can display local time with GPS-based accuracy. I F YOU BUILT the GPS-Based Frequency Reference described in the March-May 2007 issues, you’ll know that it provides a continuous readout of “Universal Time Coordinated” (UTC) on its LCD. This time is derived directly from the GPS satellite system and is therefore very accurate. In practice, it’s not all that difficult to mentally convert UTC into local time. In most cases, you simply add or subtract a certain number of hours, depending on the nominal longitude of your local time zone and, of course, your time of year. For example to convert UTC into Eastern Australian Standard Time, you simply add 10 hours, or 11 hours during the summer months when we’re on “Summer Time” (daylight saving). So 05:15:00 UTC becomes 15:15:00 (3:15pm) EAST, siliconchip.com.au or in summer 16:15:00 (4:15pm). That’s all well and good but most people would find a direct readout of their local time a little more useful. And that’s where this project comes in. It uses the 1pps (one pulse per second) output from the GPS system to drive a quartz wall clock. All you have to do is set the display for local time at the start, after which the clock will be accurately controlled via the GPS seconds pulses. It turns out to be very easy to interface the GPS Frequency Reference to a standard ‘analog’ quartz clock movement. First, you have to remove the existing circuitry from the clock (usually just a chip and a crystal on a tiny PC board) and bring out the connections to the clock’s escapement coil. That done, the coil can be pulsed instead by the little driver module described here. This driver module is small enough to fit inside the clock (next to the movement) and gets its power from the GPS Frequency Reference, along with the 1Hz (1pps) pulses. How it works If you remove the back from a standard ‘analog’ quartz clock movement and take a look inside, you’ll find a small PC board with a single IC chip and a tiny quartz crystal (usually 32.768kHz). This drives a simple stepper motor coupled to a multi-stage reduction geartrain. Inside the IC there’s an oscillator stage which uses the crystal to generate the 32.768kHz ‘clock’ pulses plus a counter chain which divides these pulses down to 1Hz (one per second). These 1Hz pulses are then used to drive the movement’s stepper motor so that it gives an increment of rotation every second. The geartrain then steps down these increments in the motor spindle’s rotation to drive the spindles for the clock’s second, minute and hour hands. The stepper motor is basically the interface between the electronic and mechanical sections of the clock movement. And that makes the motor quite March 2008  91 ANTRIM TRANSFORMERS manufactured in Australia by Harbuch Electronics Pty Ltd harbuch<at>optusnet.com.au SOFT IRON STATOR LAMINATIONS A STATOR COIL WINDING B Toroidal – Conventional Transformers Power – Audio – Valve – ‘Specials’ Medical – Isolated – Stepup/down Encased Power Supplies MULTI-POLE PERMANENT MAGNET ROTOR WITH PINION GEAR S S N N (a) BasicN Stepper Motor – At Rest A CURRENT PULSE B (N) Encased Power Supply 9/40 Leighton Pl, HORNSBY 2077 Ph (02) 9476 5854 Fax (02) 9476 3231 This kit makes a great controller for use on small electric vehicle projects, such as electrically assisted bikes and go-carts. We have tested it to over 30 amps without problems—it barely gets warm! Item code: SPEEDCON. We also have solar maximiser kits, Luxeon LEDs, and lots of interesting products and publications. Go to shop.ata.org.au or call us on (03)9639 1500. 92  Silicon Chip N A CURRENT PULSE B (S) MAGNETIC FLUX IN STATOR DURING PULSE N (N) (N) N This controller allows you to vary the speed of DC motors from 0 to 100%. It is also ideal for controlling loads such as incandescent/halogen lamps and heating elements. (b) After First 'Odd' Seconds Pulse S If you need to control 12 or 24 volt DC motors and want a speed controller that will easily handle 30 amps, then this is the kit for you. (S) S Want a real speed controller kit? (S) N Harbuch Electronics Pty Ltd S S www.harbuch.com.au MAGNETIC FLUX IN STATOR DURING PULSE (c) After Next 'Even' Seconds Pulse Fig.1: a clock stepper motor uses a multi-pole permanent magnet rotor which rotates inside a circular gap in a soft-iron stator. It’s made to step in the same direction by reversing the polarity of the current pulse at each step. interesting, especially as it’s surprisingly simple in construction. In most cases, the motor is similar to the arrangement shown in Fig.1. As can be seen, it has a multi-pole permanent magnet rotor which is free to rotate inside a circular gap in a soft-iron stator. The latter has two pole pieces which are driven by a single coil. The trick is to get this very simple motor to rotate in 1-second steps, all in the same direction. That’s done by applying the pulses to the stator coil with alternate polarity, as shown in the diagram. Basically, ‘odd’ pulses are applied with one polarity, while ‘even’ pulses are applied with the opposite polarity. As a result, the rotor clicks around through an angle equivalent to the distance between its permanent magnet poles each second – see Fig.1. The geartrain steps down these 1-second jumps to drive the clock hands! siliconchip.com.au REG1 78L05 +5V OUT GND 47 F 16V 100nF +12V IN 47 F 16V 0V (GND) IC1: 4093B 1pps INPUT 14 5 8 4 10 9 6 IC1b 100k IC2: 4013B Q CLK Vdd 13 Q CLK R 10 S Q IC1d 11 D Q R Vss S 4 7 6 6 8 3 10nF 1 CLOCK COIL +5V 1 2 7 IC1a 3 7 6 8 3 IC4 555 2 5 10nF 78L05 SC 2008 1PPS CLOCK DRIVER COM IN Circuit details Refer now to Fig.2 for the complete circuit details. It can basically be divided into two logical sections. The first section comprises the NAND gates of IC1 and flipflop IC2a. This section separates the stream of 1Hz pulses coming from the GPS Frequency Reference into two streams of alternating ‘odd’ and ‘even’ pulses. The second section comprises 555 Semiconductors 1 4093B quad CMOS Schmitt NAND (IC1) 1 4013B dual CMOS flipflop (IC2) 2 555 timers (IC3,IC4) 1 78L05 low-power 5V regulator (REG1) Resistors (0.25W, 1%) 1 100kW 1 390W OUT Fig.2: the circuit uses NAND gates IC1a-IC1d and D-type flipflop IC2a to separate the incoming 1Hz pulses into alternating “odd” and “even” pulse streams. These pulse streams then drive IC3 & IC4 which in turn drive the clock coil. This means that using the 1Hz pulses from the GPS Frequency Reference to drive such a clock movement is quite easy. All we have to do is provide a simple driver circuit which accepts the 1Hz GPS pulses and in turn applies brief current pulses to the stepper motor coil in the same alternate-polarity manner as the normal clock electronics. And that’s exactly what we do in this project. 1 PC board, code 04103081, 46 x 38mm 5 PC board terminal pins Capacitors 2 47mF 16V RB electrolytic 1 100nF monolithic ceramic (code 104 or 100n) 2 10nF monolithic ceramic (code 103 or 10n) 4 1 8 390 5 2 2 12 4 IC3 555 1 IC2b 11 7 13 IC2a 5 D 12 14 3 9 IC1c Parts List timers IC3 & IC4. These drive the stepper motor coil using the two separated pulse streams. In greater detail, the incoming 1Hz pulses are first fed through IC1b which is connected as an inverting input buffer. Note that pin 6 of IC1b is tied to ground via a 100kW resistor to prevent it from ‘floating high’ if the input cable is disconnected from the Frequency Reference. IC1b’s output appears at pin 4 and is fed in two directions – to pin 9 of IC1c and to the clock input (pin 3) of IC2a. IC1c simply re-inverts the signal and its pin 10 output is then fed to pin 12 of IC1d and to pin 1 of IC1a. IC2a is one half of a 4013B dual D-type flipflop (the second flipflop in the IC is not used here). As shown, its Q-bar output is connected back to the D input, so the flipflop is configured in toggle mode. As a result, its Q and Q-bar outputs (pins 1 & 2 respectively) toggle back and forth in complementary fashion, in response to the incoming pulses. IC2a’s Q output is fed to pin 13 of IC1d, while its Q-bar output goes to pin 2 of IC1a. As a result, IC1d and IC1a separate the 1Hz pulses into two alternating streams, each controlled by the toggling outputs of IC2a. The ‘odd’ 1Hz pulses (inverted) emerge from pin 11 of IC1d, while the ‘even’ pulses (also inverted) emerge from pin 3 of IC1a. These two separated pulse streams are then used to trigger 555 timers IC3 & IC4 which are used here simply as inverting drivers. As you can see, the clock’s stepper motor coil is connected between their two pin 3 outputs via a 390W current limiting resistor. During the gaps between the pulses, both IC3 and IC4 are in their ‘off’ state, with their pin 3 outputs both switched low. As a result no current flows through the stepper motor coil. However, each time a pulse arrives at IC1b’s pin 6 input, either pin 11 of Resistor Colour Codes o o o siliconchip.com.au No. 1 1 Value 100kW 390W 4-Band Code (1%) brown black yellow brown orange white brown brown 5-Band Code (1%) brown black black orange brown orange white black black brown March 2008  93 IC2 4013B 100k IC1 4093B IC3 555 390 47 F + REG1 78L05 + +12V ERJ 1PPS 10nF CC1 FROM GPS FREQUENCY REFERENCE 1PPS GND CC2 TO CLOCK COIL IC4 555 100nF 1 8 0 3 01 4 0 10nF GND +12V 47 F Fig.3: install the parts on the PC board as shown in this layout diagram and the photo at right. Take care with component orientation when installing the ICs and the electrolytic capacitors. IC1d or pin 3 of IC1a will pulse low, depending on the current state of flipflop IC2a. This causes either IC3 or IC4 to trigger, pulsing its output pin to the +5V level for the duration of the pulse (about 100ms) and hence driving a pulse of current through the stepper motor coil in one direction or the other. The next pulse (about 900ms later) then triggers the other 555 output driver, resulting in a current pulse through the coil in the opposite direction. Power for the circuit can be derived from any 12V DC source, including the 12V DC rail used to power the GPS Frequency Reference. This is applied to a low-power regulator (REG1) which delivers a +5V rail to power the circuit. The two 47mF capacitors and the 100nF capacitor provide supply decoupling and filtering. Building the module All of the driver module circuitry is mounted on a small PC board coded 04103081 and measuring just 46 x 38mm. This is small enough to mount in the back of most wall-type quartz clocks, alongside the movement. Fig.3 shows the assembly details. No particular order need be followed but we suggest that you install the wire link first, followed by PC stakes at the five external wiring points. The two resistors and the capacitors can then go in. Take care to ensure that the two 47mF electrolytics are orientated correctly. That done, you can install regulator REG1 and then complete the assembly by soldering in the four ICs. Be sure to orientate the ICs as shown on Fig.3 (ie, with pin 1 at lower left) and be careful not to get IC1 (4093B) and IC2 (4013B) mixed up. The two terminal pins on the left marked CC1 and CC2 are used to terminate the leads from the clock’s stepper motor coil (see below). In addition, you have to make three connections to the GPS Frequency Reference – ie, +12V, GND and the 1Hz GPS pulses. A length of 2-pair telephone cable can be used for these connections. Modifying the movement It’s not difficult to modify the quartz clock movement so that it can be driven by this module. The first step is to remove the back and then the clock’s PC board. The latter usually fits into a slot at one end of the movement’s case. If the battery contacts are attached directly to the PC board, these can be removed as well. As you are removing the PC board, you’ll find that there are two fine wires from the stepper motor coil soldered to it. These two wires must be carefully desoldered from the board, after which the board can be discarded. The next step is to connect a short length of light-duty 2-core cable (eg, a 200mm length of rainbow cable) between the coil wires and the CC1 & CC2 terminals on the driver board. This should be done in such a way that neither the joints nor the coil wires The leads from the clock coil are soldered to two pads on a piece of scrap PC board as shown in the above photo (see text). These pads also terminate the leads from the driver board. The photo at right shows the completed driver module mounted in the back of the clock case. 94  Silicon Chip siliconchip.com.au The driver board can be connected to the GPS Frequency Reference via a length of 2-pair telephone cable fitted with a DB-9 plug. This can plug into a matching DB-9 socket mounted on the rear panel, just above the “GPS 1Hz” output socket. will be strained if the lead wires are accidentally pulled. The way to do this is as follows. First, cut a small rectangle from an old PC board, making it exactly the same size as the clock PC board (so that it will slide into same case slot). That done, cut a 3mm hole into the side of the movement case near the board slot, then bring the ends of the lead wires in through the hole and solder them to two pads on the new “termination board”. Finally, solder the coil wires to these same pads and refit the back to the clock movement. The driver module itself can be mounted next to the clock module. In our case, the module was attached to the wooden dial ‘plate’ using a pair of 6G x 9mm self-tapping screws, with an M3 nut and flat washer under each to act as spacers. GPS reference connections As mentioned above, a length of 2-pair telephone extension cable is used to connect the driver module to the GPS Frequency Reference. To do this, we suggest fitting an extra DB-9 socket on the rear panel of the GPS Frequency Reference, just above the holes for the GPS 1Hz and phase error pulse outputs – see photo at left. That done, use three short lengths of hook-up wire to make the connections inside the unit to three of the pins on this added socket. One lead goes from the socket to the main board ground, another to the +12V line and the third wire to the rear of the “GPS 1Hz” output socket. Now fit a matching DB-9 plug to the end of the cable from the clock driver module. Be sure to connect the leads to the correct pins on this plug, to mate with those on the new DB-9 socket. It’s now just a matter of testing it out. Connect the DB-9 plug to the socket, apply power and check that the clock immediately starts ticking. Its second hand should step in time with the flashes from the “GPS 1Hz” LED on the GPS Frequency Reference. All that remains when you get to this stage is to set the clock movement to the current local time. If you want the second hand to read correctly as well, the easiest way to do this is to first unplug the clock connection from the rear of the GPS Frequency Reference when the seconds hand is in the 12 o’clock position. That done, set the minutes and hours hands manually for the start of the next minute and then, as soon as the UTC seconds display on the Frequency Reference’s LCD reaches “59”, plug the connection back in again to restart the clock. If you time this reconnection correctly, the clock will now display local time accurately (to the second) – and will continue to do so as long as GPS SC 1Hz pulses keep arriving. “I’ll GO THE RIGOL ... 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