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)
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.
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This design is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.
