Couter: EP frequncy counter
@7/30 2012,
ALL right reserved.
Equal precision counter block diagram
This is the most decent, High Performance device i ever design till now. the project completed about 1 years ago, around July, 2011, after a year using, it's time to say, it's my successful first step toward to RF world.
12.288Mhz TCXO reference clock. highest reference clock: 50Mhz
1Hz resolution up to 120Mhz, without pre scaler.
Equal precision design, avoid +-1Hz, sustaining same precision all the way.
base on AVR mega8 chip
High speed digital process chip for all counter parts. TI 74HC series, work frequncy up to 120Mhz.
28bit hardware counter. reference clock 24bit hard ware counter.
built with SMT, PCB size 10cmx6cm
equip with high resolution L/C meter accessory.
Module design,separated pre-amplifier board.
The frequency counter is the most easy thing to built for me, and would be the lab grade instrument. it's so useful.
How the Frequency meter works
The counter board
counter board is the core of whole project. basic idea is 2 identical counter for reference clock and the DUT clock. And time gate is control by DUT signal's raise/down edge. so
DUT frequncy= (dut counter)/(reference counter) x reference clock frequncy
using a 12Mhz reference clock ensure 1-10Mhz DUT system error < 1HZ. in practical using, 1-10Mhz crystal oscillate had no +-1HZ jump in short time.
Reference clock counter
IC5,IC1A,IC1B form a high speed percale but keep the cycle number,this it to say, no precision loss.
DUT frequncy counter
identical to reference counter, but the 74F74 IC4A, control the gate of sample period. to ensure start/stop at DUT's edge pulse.
Control board
mega8 had a 16bit counter and a 12bit counter, cascade with hardware pre-counter form a 28bit counter for DUT and a 24bit counter for reference clock.
The Counter PCB
The 3 wire LCD board
utilize the 595 chip, a serial to parallel LCD driver.
Amplifier and Pre-scaler board
LC meter
this the clone of famous LM311 LC meter. reference:
Home brew PCB: perfect hole alignment
Look, how perfect double side PCB hole is alignment!! even better than some factory grade. This is the secondary board i made for this meter.
Initial Testing
Boxing Stage 1
Boxing stage 2
LM2576 Power Board
@April/25 2016
the old instrument box have a power transformer provide 18V output, this LM2576 DC-DC convert it to 7V output, high efficiency and 500mA auto recover fuse protection.
