# Pulse counter using Digital IC and 7-seg display.

Discussion in 'Analog & Mixed-Signal Design' started by yesilovethis, Sep 7, 2016.

1. ### yesilovethis Thread Starter New Member

Jul 28, 2016
23
2
Hi all,

As a part of Hobby I made a VLF receiver which can detect close and distant thunder strikes (which are broadband spikes in the waterfall display). I want to extend that project by adding a counter to count those spikes per second (which usually range from 1 to 10). This would need usage of digital ICs, BCD to 7seg IC which unfortunately I don't remember now (I learned it during my masters but forgot due to no use in my current career).
The scheme is straight forward and seems do-able. I have attached the block diagram (the wiring is abstract as I don't remember the ICs). Only first stage is done (the receiver). The next step (starting from clipper) I am having trouble with to start. Please have a look and advice me how can make it, and what ICs ar e needed. I want to count pulse per second, not continuous. If you have/propose a schematic/circuit for this project, please let me see.
Many thanks.

2. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
909
This diagram is from a U. Arizona lecture series:

Although that diagram is from the VHF band, one can probably assume VLF will be similar. Thus, if you want to count lightning events, you may want to add two things:
1) A threshold detector (e.g., comparator) to remove the small stuff; and
2) A blanking period and/or pulse width detector so you only count a strike (e.g., cloud-to-cloud or cloud-to-ground) once. Unless, of course, you want to include return ground-to cloud and all other activity.

Ten strikes per second seems like a lot of activity for a single area, unless that includes all of the return strikes. I do not have a schematic for your project; however, AMS makes a lightning detector (AS3935) that effective does what you are trying to do. It operated at 500 kHz. I can understand the desire to DIY, but the datasheet for that device might give you some ideas.

John

Last edited: Sep 7, 2016
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3. ### yesilovethis Thread Starter New Member

Jul 28, 2016
23
2
Hi John,
Thanks for the informations. I would go through them. I can buy stuff saving money from my scholarships but there is an extreme happiness when DIY thing works (it has not be perfect, professional grade, it just need to work). I hope you get the thrill I am talking about. Besides, I have tons of spare parts (transistors, registors, diode, through hole ICs) which my University labs throw away anyway. So its a little more fun to use those old (but working) spares to make hobby things that works.
I have to do some googling with the threshold detector and pulse width detector (unless you also have some links for them, then it would be more nice).

-Ryan

Jun 4, 2014
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5. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
909
Ironically, the first commercial, airborne detector was called the Ryan Stormscope. You are in good company.

Unfortunately, the algorithms for that device and its subsequent iterations are guarded secrets. Even the AMS chip does not disclose its algorithm. However, there is a lot of information on the internet dating back many decades on lightning detection, as it is important for many purposes. U. Arizona has a prominent place in such studies, and the entire series of lectures from its spherics course is on the Internet.

I recently completed an emulator as described in the AMS application note and will be using that to test my ideas. In fact today, I am moving some code I had for reading and writing an SPI device to adapt it to reading and writing to the AS3935 chip.

John

EDIT: I was browsing my files and came across these:
http://www.techlib.com/electronics/lightning.html (simple with pulses output)
http://www.techlib.com/electronics/spherics.htm (little more complex version of "simple")

You may find them of interest. John

Last edited: Sep 7, 2016
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6. ### Bernard AAC Fanatic!

Aug 7, 2008
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74C926, 4 digit counter with 7 seg. display driver.
74C48, BCD to 7 seg. 74C90, BCD counter.
About 1980 I made some lightning detectors to stop false alarm s, used no inductors, a 4558 OP amp, a 555, & 2 ft. ant. Could not find schematic.

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7. ### yesilovethis Thread Starter New Member

Jul 28, 2016
23
2
Thanks for the IC numbers. I would look up my university lab. I hope I find them in the box labeled Digital ICs.

8. ### yesilovethis Thread Starter New Member

Jul 28, 2016
23
2
Yes, Techlib website is really nice. I followed the VLF receiver circuit from there. Although the transistors I used are different. But it works

9. ### Bernard AAC Fanatic!

Aug 7, 2008
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Also other logic families:
CD4518, 2 X 4 bit BCD; 74HC4511 & CD4511,
BCD decoder, latch,7 seg. driver.
More BCD counters: 74HC160, 74HC190, 74HC390, might find some under 74HCT---.

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10. ### yesilovethis Thread Starter New Member

Jul 28, 2016
23
2
Hi,

The gentleman in our experimental lab kindly gave me the following ICs: HCF4518BE and 74LS49N and also told me to ask anything else if I needed. But I think I can start working on my project with these two ICs. Looking at the data sheet of HCF4518BE, I see that the input can be anywhere between -0.5 to Vdd+0.5 volts. So if I have a pulse of 500mV to 1Volt (from output of my VLF receiver) then it should increase the count according to the truth table in that datasheet? Or do I have to add an amplifier to make the pulse to be around 5volt before connecting it to the clock input pin (or the enable pin) ? Please let me know how to wire up the counter IC (I hope I can connect the 7seg driver ic to 7seg, but you may also suggest the wiring if you like to help).

Thanks,
-Ryan

11. ### eetech00 Active Member

Jun 8, 2013
679
116
Hi

What is the frequency of the output pulse from the VLF receiver?
You could use a comparator to convert the 500mv-1v pulse to a logic level pulse.

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12. ### dl324 Distinguished Member

Mar 30, 2015
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What does the datasheet give for $\small V_{IH}$ for the supply voltage you're using? Does your receiver output satisfy that requirement?

13. ### yesilovethis Thread Starter New Member

Jul 28, 2016
23
2
Yes I got a comparator LM311n. Which can change even low as 200mV signal to logic level. I will use this IC.

14. ### Bernard AAC Fanatic!

Aug 7, 2008
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For decoder I find Vcc 5 V, low in 0-.8 V, hi 2-5 V., open collector output @ 8 mA.& expensive.
Counter, lo, 0- 1.5, hi, 3.5 - 5 V.
In John's display looks like a strike with follow ons = about 271 ms., so I would use the LM311 to give a neg. pulse feeding a 555 OS to blank out following signals for 1/2 sec.+/- . Will need 2 decoders for a count of 99.

15. ### eetech00 Active Member

Jun 8, 2013
679
116
Hi

Pulse output--->CMP--->Up/CNT---BCDTo7--->7SegDisplay
.................................|--->Up/CNT---BCDTo7--->7SegDisplay

If you use CD4000 series digital chips you can run everything using a 9v supply.
Also, need a 9v regulator.

16. ### Bernard AAC Fanatic!

Aug 7, 2008
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I thing it should look something like this:
Not able to bread board as IC's not in my inventory.

17. ### CuriousOne New Member

Sep 4, 2016
8
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Maxim has dedicated IC for that - ICM7217.

18. ### Bernard AAC Fanatic!

Aug 7, 2008
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I found the first error; inputs to U1 are reversed; input from detector should go to pin 3, neg., pot wiper to pin 2,
pos. Example : pot at .5 V, input grass pulses .1v; U1+ is more + than - input, the output will be high. A pulse of .6 V comes in, output will go low, triggering 555. 4 more pulses come in within .3 sec. but are ignored by 555. Pulse will be counted, outputs b & c go low lighting up seg. b & c. Displays are common anode, color unknown.
Found another; U3-10 duplicated.
Note that U3 is configured for + clock & U4 configured for - clock.

Last edited: Sep 11, 2016
19. ### eetech00 Active Member

Jun 8, 2013
679
116
What is the 555 for?

20. ### Bernard AAC Fanatic!

Aug 7, 2008
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Relook at posts 2 & 14. For a single event there might be 1 to 6 detected pulses which would give a erroneous
strike count. When triggered, a 555 will not respond to further triggers until it times out.