The TADD-2 Mini (or “T2-Mini”) is a tiny frequency divider board that accepts a 1, 2.5, 5 or 10 MHz input signal and generates a 1 pulse-per-second (“PPS”) output pulse. The pulse can be synchronized to an external source (such as a GPS receiver). The divider is implemented in a DIP-socketed PIC chip using software written by Tom Van Baak. The source code is freely available, and other software loads are available from Tom’s web site to implement different division ratios.
Tests indicate that the jitter is in the range of 1 picosecond — near the noise floor of the best test systems we’ve been able to configure. The input circuit is a wide-range design that works with signals from -20 to +13 dBm. The input may be high impedance, or terminated in 50 ohms via a jumper.
The T2-Mini has a single low-impedance output that delivers greater than 3.5 volts into a 50 ohm load, with rise time at the connector of less than 3 nanoseconds. In addition to the primary output, optional headers on the board provide either an LED or an auxiliary TTL-level output signal, and an inverted TTL-level pulse.
Power input is from 9 to 15 volts and current draw is from 20 to 50 milliamps, depending on output load.
An 8-pin header provides direct access to four of the PIC’s pins; these may be used for configuration or additional input signals. The pre-programmed PIC that TAPR provides uses the 8 pin header to allow selection of four input frequencies — 1, 2.5, 5, or 10 MHz — and synchronization of the divider to an external clock source.
The board is only 0.75 by 2.0 inches and uses surface mount parts, although the PIC chip is a socketed 8 pin DIP to allow easy reprogramming.
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