projects / unix-history / blame
| Commit | Line | Data |
|---|---|---|
| 09169146 GW |
1 | Gadget Box |
| 2 | ||
| 3 | The gadget box is a 5"x3"x2" aluminum minibox containing level-converter | |
| 4 | and modem circuitry and intended for use with host time servers | |
| 5 | supporting the Network Time Protocol. It includes two subcircuits. One | |
| 6 | of these converts a TTL positive edge into a fixed-width pulse at EIA | |
| 7 | levels and is for use with a timecode receiver or oscillator including a | |
| 8 | TTL one-pulse-per-second (1-pps) output. The other converts the timecode | |
| 9 | modulation broadcast by Canadian time/frequency standard station CHU | |
| 10 | into a 300-bps serial character stream at EIA levels and is for use with | |
| 11 | the clk_chu.c or clk_chu_STREAMS.c modules in the xntp3 distribution. | |
| 12 | ||
| 13 | This archive contains complete construction details for the gadget box, | |
| 14 | including schematic, parts list and artwork for a two-sided, printed- | |
| 15 | circuit board. All files are in PostScript, with the exception of this | |
| 16 | file and an information file, which are in ASCII. The artwork is in the | |
| 17 | 1:1 scale and is suitable for direct printing on photographic resist for | |
| 18 | each side of the board. While a plated-through-holes process is most | |
| 19 | convenient, it is possible to bridge the two sides using soldered wires | |
| 20 | where necessary. | |
| 21 | ||
| 22 | Following is a brief functional description of the device. See the | |
| 23 | schematic diagram gadget.s01 for reference. The audio output of a | |
| 24 | shortwave radio tuned to CHU at 3330, 7335 or 14670 kHz is connected to | |
| 25 | J2. A level of at least 30 mV peak-peak is required, such as provided by | |
| 26 | the recorder output on many receivers. The input level is adjusted by | |
| 27 | potentiometer R8 so that the timecode modulation broadcast at 31-39 | |
| 28 | seconds past the minute reliably lights green LED1, but the signals | |
| 29 | broadcast during other seconds of the minute do not. | |
| 30 | ||
| 31 | Opamp U4A provides low-impedance drive for the bridged-tee bandpass | |
| 32 | filter U4B. The filter has a bandpass of about 600 Hz at the 6-dB points | |
| 33 | and a center frequency of about 2150 Hz. It is designed to avoid | |
| 34 | aliasing effects with receivers of relatively wide bandpass | |
| 35 | characteristics. The modem itself is implemented by U2 and its | |
| 36 | associated circuitry. Resistors R4 and R1 are a 40-dB pad which matches | |
| 37 | the filter output to the modem input. U2 is a TTL/EIA level converter | |
| 38 | with integral power supply for bipolar signals. The modem output is | |
| 39 | available at pin 3 (receive data) of DB25 connector J1. | |
| 40 | ||
| 41 | The TTL 1-pps signal is connected via J3 to a retriggerable one-shot | |
| 42 | U3A, which generates a TTL pulse of width determined by potentiometer | |
| 43 | R7. The pulse width is determined by the bit rate of the attached serial | |
| 44 | port. In the common case the width is one bit-time, such as 26 us for | |
| 45 | 38.4 kbps, for example. This appears to the port as a single start bit | |
| 46 | of zero followed by eight bits of ones and a stop bit of one. The second | |
| 47 | one-shot U3B generates a 200-ms pulse suitable for driving the amber | |
| 48 | LED3 as a visual monitor. The output of U3A is converted to EIA levels | |
| 49 | by U1 and appears at pin 12 (secondary receive data) of J1. | |
| 50 | ||
| 51 | If only the 1-pps circuit is required, U2 and U4 can be deleted and the | |
| 52 | gadget box powered from the EIA modem-control signal at pin 20 (terminal | |
| 53 | ready) of J1, assuming this signal is placed in the on (positive | |
| 54 | voltage) condition by the computer program. J1 is wired to keep most | |
| 55 | finicky UARTs and terminal-driver programs happy. If the CHU circuit is | |
| 56 | required, an external 12-volt AC transformer or 9-12-volt DC supply | |
| 57 | connected to J4 is required. Red LED2 indicates power is supplied to the | |
| 58 | box. | |
| 59 | ||
| 60 | Following is a list of files included in this archive. All files are in | |
| 61 | PostScript, except this one (README) and the information file | |
| 62 | (gadget.lst), which are in ASCII. The files gadget.s01, gadget.s02 and | |
| 63 | gadget.lst were generated using the Schema schematic-capture program | |
| 64 | from Omation. The printed-circuit files *.lpr were generated using | |
| 65 | Schema-PCB, also from Omation. | |
| 66 | ||
| 67 | Files | |
| 68 | ---------------------------------------- | |
| 69 | README this file | |
| 70 | gadget.s01 circuit schematic | |
| 71 | gadget.s02 minibox assembly drawing | |
| 72 | gadget.lst net list, pin list, parts list, etc. | |
| 73 | gen0102.lpr pcb x-ray diagram | |
| 74 | art01.lpr pcb artword side 1 | |
| 75 | art02.lpr pcb artwork side 2 | |
| 76 | adt0127.lpr pcb assembly drawing | |
| 77 | dd0124.lpr pcb drill drawing | |
| 78 | sm0228.lpr pcb solder mask (side 2) | |
| 79 | sst0126.lpr pcb silkscreen mask (side 1) | |
| 80 | ||
| 81 | Dave Mills | |
| 82 | University of Delaware | |
| 83 | 6 July 1992 | |
| 84 | Revised 21 August 1992 |