4017 decade counter questions - Page 1
Forum section: electronics / beginners

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 13, 2014, 03:44:59 pm
content: I am building something which to me, as a beginner is quite complex. As such I am trying to build sections of the circuit on a breadboard in order to better understand how it all works. It is also a sanity check to see what, if anything I am doing wrong, at a basic level. I have hit an immediate issue, which I do not understand and need some guidance please. I have hopefully attached a schematic at the end of my post, and if it doesn't work, also a link. I am initially looking at just IC2, the 4017 decade counter. I have put in my breadboard and fed it various square and sine waves from my signal generator at pin 14 and ground. I am looking at the output from pin 2 and ground with my `scope and a frequency counter. The circuit I am building appears to run a regulated 12V to the CMOS stuff. But when I run anything over about 6V the frequency out from 2 and ground is no longer divided down to 274kHz, but is at the 1.37MHz input frequency. I have tried various input levels from my sig gen, from 0.1V peak to peak to 5V peak to peak with the same result dependent on the voltage fed to the chip. Increasing voltage to the chip up to about 6V gives a rising output amplitude, then around circa 6V the scope trace suddenly changes and once it settles I get 1.37MHz out the 4017. Operating at lower input frequencies it does the same thing, so I don't think it's all the log wires and limitation of breadboard construction at the higher frequencies. What am I misunderstanding please, as this appears to be a circuit feeding a full 12V to the 4017. Thanks. I have literally just created IC2 and power to it, on the breadboard, linked pins 8 and 13 to ground, linked pins 1 and 15, applied the input to pin 14 and ground, and taken the output from pin 2 and ground. Then applied 3 to 12 V to pins 16 +ve and 8, 13 -ve. Puzzled...I am suspecting the trailing wiring, but not sure.http://www.gatesgarth.com/amp.doc

author: fcb
author_rank: Super Contributor
timestamp: December 13, 2014, 04:10:45 pm
content: It's difficult to read your posting, and I won't open .doc's from the web.Can you put some spacing into your question, and upload a JPG/PNG or PDF.

author: mij59
author_rank: Frequent Contributor
timestamp: December 13, 2014, 04:27:26 pm
content: Hi,The input of the CD4017 requires logic voltage levels ( 0 or 12 V) with a fast transition between the logic levels.

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 13, 2014, 04:38:26 pm
content: So if I preceded it with IC1a, the HEF4001 it would then drive it correctly?I upped my signal generator to maximum peak to peak, which is 10V and it now dividescorrectly when the 4017 is fed 12V! Thanks for helping!I attach a .jpg of the schematic for the more paranoid amongst usIs it the line length people find hard to read? I don't think it's mypunctuation, my English is infinitely better than my electronic skills

author: mij59
author_rank: Frequent Contributor
timestamp: December 13, 2014, 04:49:20 pm
content: IC1a is configured as an analog amplifier, probably works.Not the most elegant solution.

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 13, 2014, 05:20:13 pm
content: Ok, thanks for that. I now realize that the 4017 needs different drive levels dependent on the voltage applied to the device. Is that typical of all these sort of things?

author: dannyf
author_rank: Super Contributor
timestamp: December 13, 2014, 05:33:15 pm
content: QuoteTake a look at the device's datasheet: it should define the min/max levels for logic high / low under different supply voltage levels. A safe rule is 80/20: drive to 80% of Vcc for '1' and 20% of Vcc for '0'.

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 13, 2014, 05:47:00 pm
content: OK thanks, will do, I see they have this specced, hadn't quite understood the significanceuntil now, so breadboarding and playing *IS* teaching me quite a bit, had I just built it Iwould have not understood the nuances of it!I have been given an alternative idea, and that's to use my TS-590 set to TX at 2.74MHz as thedriver, and then divide by 10. I have the 4017 reliably dividing by 5 with my sig gen maxxed out,and 12V on the 4017. Not sure how to reconfigure it to divide by 10 though, will have a play!Many thanks!

author: SeanB
author_rank: Super Contributor
timestamp: December 13, 2014, 06:03:29 pm
content: You are running into one of the 4017's quirks in that you need to stretch the pulse that you use to reset the counter slightly, otherwise it may not reset properly. Use the rest of IC1 as a buffer, and add a small RC delay to it, then use in the link between pins 1 and 15. That way you have a longer pulse from the reset circuit which will both properly reset the IC and will give a longer length pulse output as well. To connect pin 1 is an output to the input of the nor gate and pin 15 is the reset. RC will probably be 100R and 100pF.To divide reliably by 10 you just connect reset to gnd and use the carry out on pin 12, as this has a roughly 50% duty cycle and is meant to give a divide by 10 directly.

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 14, 2014, 04:40:01 pm
content: Thanks SeanB, sadly I had not fully appreciated the fact that manydigital modes, like WSPR and OPERA that are popular on the LF bandsdo not take kindly to having their bandwidth divided by 10, so althoughI now have my frequency out at 174kHz, and working well, this decimation ofthe overlaid signal stops the message passing correctly. I am told by those thathave faced this same issue the answer is to *MULTIPLY* the output of my transceiverup to around 274kHz, bypass the divide by 5 or 10 stage, but utilise the requireddivide by 2 stage top get the push pull output to drive the PA FETS. Thisfrequency multiplication does not affect the overlaid message modulation bandwidths.I am afraid i will be making a new post on how to go from 136kHz at 0dBM to about10 to 17dBM to drive the multiplier circuit. Thanks again, learning a lot here!

author: dannyf
author_rank: Super Contributor
timestamp: December 14, 2014, 07:08:17 pm
content: I have to say that I don't quite understand your struggle.QuoteIt is a decade counter, isn't it? Or we are talking about something else here.

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 15, 2014, 12:30:48 pm
content: My struggle was understanding how the digital data mode WSPR-X worked modifying a carrier out, and how carrier frequency changes effect the ability of the WSPR-X signal to be de coded. I think I have my head around it now, it was partly my first introduction to decade dividers, partly my uselessness at mathematics, and partly my lack of information on how WSPR-X works.For what it's worth here's my take on things now:It took me ages and much prompting to get my head around this, but I*THINK* I have a handle on it now. Let's say I set my TS-590 to TX at2.74 MHz. WSPR effectively modifies the frequencies it transmits on by3 or 4 increments to the carrier frequency. It adds 1.46Hz each time. So ittransmits on 4 different frequencies. But when I divide the output of2.74 by 20 (divide by 10, then by 2) in the G3YXM circuitry, mycarrier is now the desired 137kHz, but the WSPR 1.46Hz "add ons" aredivided by 20 also, and are now only 0.073Hz "add ons". So no one candecode the signal.If I transmit on 137kHz via the DRV OUT socket, amplify the 0dBm signal for a multiplier circuit to use (10 to 17dBm) and multiply thatoutput by 2 times externally, the "add on" frequencies of 1.46Hz,2.92Hz, and 4.38Hz (and maybe a 4th add on if used, I am not sure), are alsodoubled. The by two divider IC4, in the G3YXM amp, then divides them by two,along with the carrier, and we are correct again at the antenna.I THINK I have this right save for how many frequency steps WSPRadds, not sure if the carrier is used without an addition is one, or if itadds 4 increments.Thanks again!