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diff --git a/contrib/ntp/html/gadget.htm b/contrib/ntp/html/gadget.htm new file mode 100644 index 0000000..80274535 --- /dev/null +++ b/contrib/ntp/html/gadget.htm @@ -0,0 +1,111 @@ +<html><head><title> +Gadget Box PPS Level Converter and CHU Modem +</title></head><body><h3> +Gadget Box PPS Level Converter and CHU Modem +</h3> + +<img align=left src=pic/gadget.jpg>A Gadget Box built by Chuck Hanavin + +<br clear=left><hr> + +<p><h4>Introduction</h4> + +<p>Many radio clocks used as a primary reference source for NTP servers +produce a pulse-per-second (PPS) signal that can be used to improve +accuracy to a high degree. However, the signals produced are usually +incompatible with the modem interface signals on the serial ports used +to connect the signal to the host. The gadget box consists of a handful +of electronic components assembled in a small aluminum box. It includes +level converters and a optional radio modem designed to decode the radio +timecode signals transmitted by the Canadian time and frequency station +CHU. A complete set of schematics, PCB artwork, drill templates can be +obrtained via the web as the distribution <a href= +"http://www.eecis.udel.edu/~mills/ntp/ntp">gadget.tar.Z</a>, or by +anonymous FTP from ftp.udel.edu in the <TT>pub/ntp</TT> directory. + +<p>The gadget box is assembled in a 5"x3"x2" aluminum +minibox containing the level converter and modem circuitry. It includes +two subcircuits. One of these converts a TTL positive edge into a fixed- +width pulse at EIA levels and is for use with a timecode receiver or +oscillator including a TTL PPS output. The other converts the timecode +modulation broadcast by Canadian time/frequency standard station CHU +into a 300-bps serial character stream at EIA levels and is for use with +the <code>tty_clk</code> and <code>chu_tty</code> line disciplines in +the ntp3 distribution. + +<p>This archive contains complete construction details for the gadget +box, including schematic, parts list and artwork for a two-sided, +printed-circuit board. All files are in PostScript, with the exception +of this file and an information file, which are in ASCII. The artwork is +in the 1:1 scale and is suitable for direct printing on photographic +resist for each side of the board. While a plated-through-holes process +is most convenient, it is possible to bridge the two sides using +soldered wires where necessary. + +<p><h4>Circuit Description</h4> + +<p>Following is a brief functional description of the device. See the +schematic diagram gadget.s01 for reference. The audio output of a +shortwave radio tuned to CHU at 3330, 7335 or 14670 kHz is connected to +J2. A level of at least 30 mV peak-peak is required, such as provided by +the recorder output on many receivers. The input level is adjusted by +potentiometer R8 so that the timecode modulation broadcast at 31-39 +seconds past the minute reliably lights green LED1, but the signals +broadcast during other seconds of the minute do not. + +<p>Opamp U4A provides low-impedance drive for the bridged-tee bandpass +filter U4B. The filter has a bandpass of about 600 Hz at the 6-dB points +and a center frequency of about 2150 Hz. It is designed to avoid +aliasing effects with receivers of relatively wide bandpass +characteristics. The modem itself is implemented by U2 and its +associated circuitry. Resistors R4 and R1 are a 40-dB pad which matches +the filter output to the modem input. U2 is a TTL/EIA level converter +with integral power supply for bipolar signals. The modem output is +available at pin 3 (receive data) of DB25 connector J1. + +<p>The TTL PPS signal is connected via J3 to a retriggerable one-shot +U3A, which generates a TTL pulse of width determined by potentiometer +R7. The pulse width is determined by the bit rate of the attached serial +port. In the common case the width is one bit-time, such as 26 us for +38.4 kbps, for example. This appears to the port as a single start bit +of zero followed by eight bits of ones and a stop bit of one. The second +one-shot U3B generates a 200-ms pulse suitable for driving the amber +LED3 as a visual monitor. The output of U3A is converted to EIA levels +by U1 and appears at pin 12 (secondary receive data) of J1. + +<p>If only the PPS circuit is required, U2 and U4 can be deleted and the +gadget box powered from the EIA modem-control signal at pin 20 (terminal +ready) of J1, assuming this signal is placed in the on (positive +voltage) condition by the computer program. J1 is wired to keep most +finicky UARTs and terminal-driver programs happy. If the CHU circuit is +required, an external 12-volt AC transformer or 9-12-volt DC supply +connected to J4 is required. Red LED2 indicates power is supplied to the +box. + +<p>Files + +<p>Following is a list of files included in this archive. All files are +in PostScript, except the <code>README</code> and +<code>gadget.lst</code> files, which are in ASCII. The files +<code>gadget.s01, gadget.s02</code> and <code>gadget.lst</code> were +generated using the Schema schematic-capture program from Omation. The +printed-circuit files <code>*.lpr</code> were generated using Schema- +PCB, also from Omation. + +<p>Files + +<p><code>README</code> - helpful information +<br><code>gadget.s01</code> - circuit schematic +<br><code>gadget.s02</code> - minibox assembly drawing +<br><code>gadget.lst</code> - net list, pin list, parts list, etc. +<br><code>gen0102.lpr</code> - pcb x-ray diagram +<br><code>art01.lpr</code> - pcb artword side 1 +<br><code>art02.lpr</code> - pcb artwork side 2 +<br><code>adt0127.lpr</code> - pcb assembly drawing +<br><code>dd0124.lpr</code> - pcb drill drawing +<br><code>sm0228.lpr</code> - pcb solder mask (side 2) +<br><code>sst0126.lpr</code> - pcb silkscreen mask (side 1) + +<hr><a href=index.htm><img align=left src=pic/home.gif></a><address><a +href=mailto:mills@udel.edu> David L. Mills <mills@udel.edu></a> +</address></a></body></html> |
