The frequency counter is a complex side circuit to the Oscillation Overthruster, so I’m putting it in a new post.

This is the final design.  There were a few mistakes in the prototype, the 1st and 3rd LED digit strobes were switched, a few capacitors that didn’t have the right lead spacing, and the logo was bad… ProtoExpress didn’t silk screen over the hole in the solder mask.  The parts are renumbered and mistakes have been corrected.

Files:frequency_counter.zip (1 MB)



Eagle 3D POV-Ray of Frequency Counter board


The POV-Ray image has some inaccuracies and missing parts, I’m just learning how to use Eagle 3D.

This circuit takes a square wave signal (0 – Supply Volts) and displays the frequency on six 7-segment LEDs, for a range of 0 – 1MHz.  It counts the pulses occurring in one second, and displays the count over the next second.  It needs a 5-15 volt regulated power source, which will be supplied by the Oscillation Overthruster.  The zip file includes the Eagle PCB CAD files, Gerber files, the bill of materials, a few PNGs of the board and schematic, and where to get the full Creative Commons license.

I tested the circuit using a 5 volt supply, but all the ICs are rated for over 15V, so a regulated 12V supply and square wave input should work just fine.

This was designed using Eagle Light version v5.20 for Linux.

Partlist exported from frequency_counter.sch

Qty Value Device Comment/Digikey Parts
5 1K 1/4 watt resistor, 10mm lead-in R2, R3, R4, R5, R7
1 1M 1/4 watt resistor, 10mm lead-in OK anywhere from
910K to 3.3M
R6
1 1nF poly capacitor, 5mm lead-in for LED driver strobe C1
3 2N2907 PNP transistor
TO-92 ( or TO-18 )
for LED digit select Q2, Q3, Q4
2 4.7nF poly capacitor, 5mm lead-in for pulse shaping C5, C6
1 4.194304MHz crystal, 5mm lead-in (49UA) X007-ND Q1
1 10K 1/4 watt resistor, 10mm lead-in for pulse shaping R8
1 22pF capacitor, 2.5mm lead-in optional, if needed C4
1 82pF capacitor, 2.5mm lead-in optional, if needed C3
3 100nF poly capacitor, 5mm lead-in for VCC to GND filtering C2, C7, C9
1 100uF electrolytic capacitor
8mm with 3.5mm radial leads
for VCC to GND filtering C8
1 4093 IC: Quad 2-input NAND
Schmitt Trigger 14-DIP
296-2068-5-ND IC3
1 4521 IC: 24 stage Frequency Divider
16-DIP
296-14158-5-ND IC4
2 14543 IC: BCD to 7-Segment
Latch/Decoder/Driver 16-DIP
MC14543BCPGOS-ND IC1, IC5
2 14553 IC: 3 Digit BCD Counter
CMOS 16-DIP
MC14553BCPGOS-ND IC2, IC6
2 LTC-4724JR LITE-ON Common Cathode
triple 7-segment LED
160-1545-5-ND LED1, LED2
2 220 (x7) 7 (or 8 ) 14 or 16-DIP isolated
resistor
LED current limiter,
can use 7
1/4 watt resistors
R1, R9

I recommend http://www.protoexpress.com for manufacturing.

Accuracy: assuming the crystal passes it’s +/-30ppm rating, that would be:
100% * ( 2^22Hz +/- (2^22Hz * (30 parts/1 MHz)) ) / 2^22Hz , right?
100 * ( 2^22 + ((2^22) * (30/1e6)) ) / 2^22 = 100.003
So that’s +/- 0.003 % maximum error.  Sounds pretty good to me.  I’m not really sure that the ( +/- 30 parts / 1MHz ) constant is the correct way to represent the error factor.  The counter chip also latches on falling edge, but the master reset on level (from what I can tell on the data sheet) so there may be some loss due to the length of the master reset pulse formed by R7 and C5.

Creative Commons License

Copyright (c) 2008 MDVE.NET. Some rights reserved.
This design is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.

One Response to “Frequency Counter”
  1. […] Energy Meter using VFC Here's a frequency counter schematic – the very first one, when you search for "frequency counter schematic" in G00gle images: […]

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