In the 4073 package, are the inputs of the unused gates tied to vdd/gnd or are they open ? They must be tied, or you may get unwanted oscillation, and also noise on other outputs (crosstalk from the oscillation).

 

I'm assuming your talking about the 4075 in the schematic (which isn't hooked up yet) that was substituted for a 4025 due to availability. there were 2 unused gates and they were properly grounded.

I may have misunderstood your question completely. however, I have in fact went through and properly grounded all unused portions of all the ic's.

 

I connected the logic portion to the random and started running the tests. first the output (pin 3) and it was moving from 0v to 12v. because I am unable to shut the random off its difficult to see any consistent results. I have to pull a 10 nF off of the other board to remove the random portion from the equation. unless you have another way to do it with uF caps...

 

I connected the logic portion to the random and started running the tests. first the output (pin 3) and it was moving from 0v to 12v. because I am unable to shut the random off its difficult to see any consistent results. I have to pull a 10 nF off of the other board to remove the random portion from the equation. unless you have another way to do it with uF caps...

It doesn't need to be 10nF. That's a commonly used value. I guess any mid sized cap will work, possibly even no cap at all.

Unless somebody works every day with 555 circuits this is just something you don't test, usually you use the value indicated in datasheets and app notes. Just try another value. Don't you have a spare 100n?

 

I have an extra 100 nF... that will work right?

 

I have an extra 100 nF... that will work right?

Yes, for the noise you are seeing 0.1uF is good. Maybe add a 220uF between the power supply + and - as well if there isn't already a larger cap on the power rails.

Every IC should have a 0.1uF/100nF cap between V+ and GND, see "Bypass Caps" link in my sigline.

 

Heres a snapshot of it at the lower voltage:
It jumps all around huh??

Yes it oscillates.

and for fear of going to 0 ohms I stopped close and here's a screen shot of the randomness:

Thanks for that . That's what I expected.

Yes, for the noise you are seeing 0.1uF is good.

Well, 100nF at pin 5 of the 555 IS good but it cannot have anything to do with the oscillation. The oscillation is at the output of the LM258. The 555 was not yet connected.
It happens near 4V, looks like the lowest level at the output of the 258, i.e all outputs of the D-FlipFlop are probably HIGH.

I'll check this tomorrow if nobody comes up with a solution.

 

I didn't do much after lunch today. tomorrow I will add that capacitor and switch so that I can turn off the random portion. when I test the outputs of the 4017 to ensure that only 1 is on at any given time, I need to devise a way to probe all the outputs 4 at a time. I was thinking of sticking pins inside the sockets of all the outputs. what do you think?

when you stated that there might be a concern with T7 being on when any other transistor is on, makes me really want to test with a resistor like you laid out earlier (post #144) but how will there be a voltage spike when nothing else is hooked up (no load) will it spike through T8? And if I understand correctly I will just have a 1k resistor between the drains of T7 and T8 and put the leads of the volt meter on each side of the resistor... I should get 0 volts at all times?

I'm on my phone right now so I can't draw a picture and post it ( if you haven't noticed I am a visual learning type person ) but I will when I get to my laptop.

I'll check this tomorrow if nobody comes up with a solution.

so that oscillation is a big concern huh?

 

I didn't do much after lunch today. tomorrow I will add that capacitor and switch so that I can turn off the random portion. when I test the outputs of the 4017 to ensure that only 1 is on at any given time, I need to devise a way to probe all the outputs 4 at a time. I was thinking of sticking pins inside the sockets of all the outputs. what do you think?

You could use only two probes and measure one after another, i.e. 1 with 2, 1, with 3, 1 with 4 etc, then 2 with 3, 2 with 4 etc and so on.
There shouldn't be a problem with the counter IC.

when you stated that there might be a concern with T7 being on when any other transistor is on, makes me really want to test with a resistor like you laid out earlier (post #144) but how will there be a voltage spike when nothing else is hooked up (no load) will it spike through T8? And if I understand correctly I will just have a 1k resistor between the drains of T7 and T8 and put the leads of the volt meter on each side of the resistor... I should get 0 volts at all times?

Not ANY other transistor, only this transistor pair. The same signal is turning one FET on and the other one off. The source terminals of both transistors are tied to the power supply rails, one to + the other to -. If both are on, that's a shortcircuit. The transistors don't have the same turn-on/turn-off time so that is something that is possible, but it shouldn't be the case because of the diode/resistor combination at the gates. This should ensure a fast turn off and a slow turn on.
If both transistors are ON, the resistor is directly connected to the power supply. This voltage you can measure , but not with a voltmeter, you need the socilloscope and choose a timebase of a few us at most.

so that oscillation is a big concern huh?

No, not for your application. I would like to know why it's there though.

 

eureka!!! I completely understand what you're saying. I will definitely check that tomorrow as well. thanks a bunch.

 

I had time before "lights out" to add the switch and capacitor, so then I was able to probe the 4017. One question that I have for you is, How fast is this going to spin, if every time there was a pulse from an output, that seems pretty fast. and I assume that every time one output pulsed the magnet would have spun 1 full revolution. Is this right?

While probing one of the outputs on the 4017, I pause the scope and counted how many times one output pulsed on 1 second sweep and it was 84 times per second with an RPM of 5040, and that was at 1 meg ohms of resistance.

Is this right? and if so, I will need a way for it to start off slower than that.

 

While probing one of the outputs on the 4017, I pause the scope and counted how many times one output pulsed on 1 second sweep and it was 84 times per second with an RPM of 5040, and that was at 1 meg ohms of resistance.

Is this right? and if so, I will need a way for it to start off slower than that.

The 555 frequency should be 15Hz, i.e. 15Hz / 6 (60 degree coils) = 2.5 RPS...

You can increase the 100n timing capacitor of the 555, e.g. 1uF or 10uF electrolytic capacitor (with "-" connected to ground)

 

I knew I must have been reading that wrong.

 

When you say 15Hz is that due to the potiometer/capacitor combonation in the circiut?

If so, to dumn things down, in order to control RPM without random portion on, I would change resistance of the 1M pot, less resistance = faster RPM and vise versa.

Another way is to change the capacitor at pin #5 to ground on the 555, a higher capacitance (10nF) will increase RPM and lower capacitance (10uF) will slow it down.

Is this correct?

 

When you say 15Hz is that due to the potiometer/capacitor combonation in the circiut?

Yes.

Another way is to change the capacitor at pin #5 to ground on the 555, a higher capacitance (10nF) will increase RPM and lower capacitance (10uF) will slow it down.

Is this correct?

No. The capacitor at pin 6 and 2 (which are tied together) in combination with the 1MΩ determine the oscillator frequency.

Increase the resistor value -» frequency decreases
Increase the capacitor value -» frequency decreases

!M is already quite high so I recommend increasing the capacitor value.

In the other post I said the capacitor value at pin 5 doesn't matter but that's not absolutely true in your case. Since you are actively driving that pin the capacitor value will have an influence, yes. But 100n at pin 5 are ok, I guess. Usually you just connect 10nF, this has no effect on frequency though.

 

Hello,

I tested the circuit around the LM258. It does not oscillate. I didn't use potentiometers though . The voltage output changes between around 8V to 2V.

I use a regulated 12V bench top power supply.

Can you tell me at what frequency it oscillates?

 

You have to school me a bit more, how do I determine frequency?, I messed around and looked through the options of the scope and it appears that I don't have anything that will tell me Hz.

 

You have to school me a bit more, how do I determine frequency?, I messed around and looked through the options of the scope and it appears that I don't have anything that will tell me Hz.

Do you have a manual of the scope?

On one picture I saw 50us in the lower right corner. I assume this to be the time per division.

If you are not sure about what you see on the scope you need a known frequency and measure it with the scope to correlate what you see on the screen with the measured frequency.

This could be easily done with a very slow frequency, e.g. 1Hz. The signal on the screen would then change every 1s.

Example: connect the probe to the power supply output and turn the power supply on one second and off the next and so on.. Adjust the scope timebase to 1s. The signal should change every division.

 

Forget the previous post. I've seen it says "sweep" where the time is indicated.

The whole screen width is equivalent to the time you see under "sweep". (that's what I understand)

 

That's how I understand it as well. to clarify then,I will set the scope to a certain time (say 50 us) probe the output of the 258 and when it get's to the 3 volts (where it oscillates) pause it and count the waves that are displayed on the screen? and by doing that, you will be able to take the 2 numbers and determine the frequency?


So I un-soldered the connection between the gates of T7 and T8, I then soldered a 220K resistor between the 2 and then I put one probe on the gate of T7 and one on the gate for T8 and this is what it displayed, channel 1 (yellow) was connected to T7 and Channel 2 is connected to T8.

I also attached the ground to T7 and a test probe to T8 and there was 11.5 volts present. Isn't that a bad thing?