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I'm a beginner in electronics and am working on a Baby10 step sequencer for a project. It consists of a 555 timer for a clock signal, a CD4017 decade counter and 2 more 555s for an Atari Punk Console for the audio part. I constructed both parts separately and they seem to be working fine(The 4017 output was sent to LEDs to visualize the selection output and the Atari Punk console too) but when I send the CV signal from the 4017 to the APC input I don't get any sound but that of a faint metrome. Should I add something like an amplifier between the CV output from the counter and the APC? Is there anything I've missed? This is the schematic I used:

enter image description here

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  • \$\begingroup\$ Hi and a warm welcome to the site, Dennis. I'm afraid the schematic is missing - please modify your question to fix it. \$\endgroup\$ – TonyM Jul 5 '17 at 20:36
  • \$\begingroup\$ @TonyM The image was referenced in the post, but not embedded properly. I've fixed this. \$\endgroup\$ – duskwuff Jul 6 '17 at 3:48
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According to your schematic, you have the CV input going directly to Pin 7 the discharge pin. Pin 7 first needs to be connected to pin 6 in the Astable Multi-Vibrator using the 1k ohm resistor.

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  • \$\begingroup\$ But it is connected in that manner in the circuit diagram right? \$\endgroup\$ – Dennis Aug 14 '17 at 15:34
  • \$\begingroup\$ After looking this over some more I think it has become a bit more obvious as I have a few 4017s now and have read the schematic. Use the Multivibrator 555 TIMER's Output to go to the Clock Signal of the 4017. Then have the timer outputs go directly to the trigger of the monostable mode.The CV input should go to the monostable's trigger and you should have a potentiometer to select the frequency of the APC where you have the CV. \$\endgroup\$ – Danny Sebahar Aug 15 '17 at 20:04
  • \$\begingroup\$ I ended up changing my schematic a bit because I had to submit my project but I got it working in another way. I just wired it as it is but removed the LEDs and their resistors and it worked! I noticed there was a large potential drop across the resistors to the LEDs and barely routed any current the other way(through the pots for CV) and probably that is why there was no sound. Bear with me because I'm a rookie but if the resistors go to the LEDs and then to ground, is there something wrong with the schematic of that part causing all the current to route that way or did I miss something? \$\endgroup\$ – Dennis Aug 17 '17 at 13:40
  • \$\begingroup\$ I thought you were using just two 555 timersWell, it's not a Current thing. The 555 Timer has two VOLTAGE Comparators in it \$\endgroup\$ – Danny Sebahar Aug 19 '17 at 14:03
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I learned a bit more about electronics in the mean time: So first, why is their no current going to the Cv output through the diodes and the pots? I know all the reasons now.

The 555 timer is called a 555 timer because it includes 3 5k Ohm resistors in a voltage divider configuration to provide not only the Threshold Voltages for the two internal Comparators, but those are the output voltages as well. So I'm guessing you are at a max of 9 Volts for Vcc (because you based it on an Atari Punk Console which uses 9-volts) and the voltage dividers High Output is 2/3rds of that so you have about 6-volts as your output and luckily that fits within the range of input voltages allowable as the 555 timer is TTL and the CD4017 is CMOS. Sometimes CMOS can't except TTL outputs but you chose a high voltage tolerant one.

So next, looking at the datasheet, a 9 Volt input results in a high (square wave high) voltage of near 9-volts as well as CMOS means high input impedance and low output impedance (Output is pulled from Vcc).

NOW HERE WAS YOUR INITIAL ISSUE: 1. You created a voltage divider with a 470,000 Ohm resistor and a 1,000 Ohm resistor. The equation for Voltage Division is R2/(R2+R1) so if the 1k resistor is R2 as The electron flow is flowing from CV, through the Diodes, through the pots, through the 1k, and then the LEDs. so in that order, R2 is 1k. and 1/471000= really damn small. So the amount of voltage going to the LEDs is near 9-Volts and the amount going to the Speakers is not large enough source .7 volts from your CV. Thus in the original, only the LEDs worked. When you removed the LEDs and resistors you removed the voltage divider. So now the Voltage could flow to the speakers. But I don't know why they are potentiometers as that would only control volume.

An ideal circuit would provide 20mA to the LEDS (.02/9=450 Ohms needed to light LEDS). An LED will drop .7 Volts and so the voltage divide needs 450 ohms to be 7% of the speaker resistors (450/.07=6,450 Ohms) This will give .7 Volts to the LEDS which will activate them at 20mA and leave the remaining 8 volts going to your Speakers 1.2 milliAmps at 8-Volts which is right at the "Typical" rating of the CD4017s Outputs.

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  • \$\begingroup\$ It seems that the bulk of this answer is a quote from a third party (Clue: NOW HERE WAS YOUR INITIAL ISSUE). It would be better to place the quote in block quote formatting, and also to credit your source with a link. \$\endgroup\$ – Greenonline Apr 21 '18 at 10:07

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