electronically controlled variable speed pulse generator?

[crosslakeguy]

I need a two speed (both high and low speed adjustable through trim pot) oscillator. to drive stepper motor pulses. right now I am using a 555 ic the low speed I have a pot where one resistor is and a relay to bring the other resistor from 1k resistor to 0 k for high speed. my motor is running anywhere from 30rpm to 300 rpm its a standard i think 1.8 degree step so 200x whatever rpm x60 for pps.

so running at 30-100rpm for low speed then around 100-350rpm for high speed
adjustable low and high, and switchable between high and low.

 

[alec_t]

If what you have 'right now' is working what do you want to change?

 

[crosslakeguy]

well....... not sure if there is a simpler way to do it? is there an IC that allows isolated resistor to be used in a circuit? I used a trim pot in series/reed relay. I looked at other forums, and someone wanted to use a series of resistors to do something similar but didn't see a solid answer. I tried a 4066 relay Ic but that did not work. I guess I was thinking about getting away from the reed relay. I know I could have just used a plc, but am not familiar wth the programming, and wanted to keep it simple. also I may want to eliminate the pots, and use an up/down button for speed control.

 

[Roff]

Post the schematic of what you have.

 

[crosslakeguy]

right now (RA) is a fixed 1k resistor and (RB) is a 1k trim pot to control speed. then added a dip relay to make 0 ohm connection between pins 6-7 (RB) which increases pulse speed as noted in osc. I think pin 7 is supposed to be the center on the trim pot then 6&8 on other sides ? I do not have it wired that way,, I have 2 seperate resistors. and was planning on using 1k trim pots on (RA) and (RB) currently using option (2) for (RB). when 0 ohms across pins 6-7 makes the high speed. It works but seems that there is a better way to do it? (the (RB) value may not be a 1k I am not home, but I think it is a 1k?

View attachment 63436

 

[Roff]

right now (RA) is a fixed 1k resistor and (RB) is a 1k trim pot to control speed. then added a dip relay to make 0 ohm connection between pins 6-7 (RB) which increases pulse speed as noted in osc. I think pin 7 is supposed to be the center on the trim pot then 6&8 on other sides ? I do not have it wired that way,, I have 2 seperate resistors. and was planning on using 1k trim pots on (RA) and (RB) currently using option (2) for (RB). when 0 ohms across pins 6-7 makes the high speed. It works but seems that there is a better way to do it? (the (RB) value may not be a 1k I am not home, but I think it is a 1k?

View attachment 63436

There are lots of ways to do this, but starting with what you have, you could replace the relay with one section of a 74HC4066, and control it with a 5 volt signal. 5V turns it on, 0V (ground) turns it off. Remember to connect pin 14 to +5V and pin 7 to ground. If you don't need the other switches in the package, put all of them in parallel, and drive all the control inputs with the same signal.
If this were my circuit, I would scale the pots up to 10k or 100k, and the 10uF cap on pin 6 down accordingly (1uF or 0.1uF). This is because you need a resistor in series with RA to protect pin 7 from a short to +5V when the pot is cranked to zero ohms. You could add 100 ohms, but that means pin 7 has to sink 50mA, which is kinda high, IMHO.

 

[crosslakeguy]

I did try to use a 4066, but could not get it to work for some reason??will a resistor feed through a 4066 as resistance? Thats why I used a relay, to isolate completely?
I can definately change the value of (RA) and (RB) and the caps for the correct balance/protection....the pulse signal is unbalanced anyways. so all that aside . is there a better way to acomplish an dual speed setup. I can get by with 1st slow speed (able to adjust speed on fly) and high speed fixed but adustable for setup/one time

 

[Roff]

The 4066 will work if you connect it correctly. The switch is isolated from the control. 74HC4066 has much lower on resistance than CD4066.
I'm assuming you want the low speed and high speed controls to be noninteractive. You need to tell us what the actual pulse frequency needs to be for , say, 300RPM.

 

[crosslakeguy]

hertz=1pps / 60,000 pps, is that 60khz? so I have used a mc104066, and think the 74hc4066 has similar values, the question remains..................
does the resistance carry through???? , you recommended changing the values of the resistors, is that because of the limits of the circuit? a mechanical relay has no resistance at all. is there a circuit that will induce a specific resistance into a circuit? , and is there a better way of a 2-speed controler? as far as interactve? not realy. same circuit, different speed low(adjustable)/switched high.

 

[Roff]

Is hertz measured in a second?: 60,000 pps, is that 60khz? so I have used a 4066, and think the 74hc4066 has similar values, the question remains..................
does the resistance carry through???? , you recommended changing the values of the resistors, is that because of the limits of the circuit? a mechanical relay has no resistance at all. is there a circuit that will induce a resistance into a circuit?

Yes, Hertz (Hz)=cycles per second. How does 60kHz relate to the RPM of your motor?
What do you mean, "does the resistance carry through"?
The 74HC4066 ON resistance is only about 50 ohms per switch. This is insignificant relative to 10k.

 

[crosslakeguy]

I put the formula in the post earlier for rmp/pps moving on.............................................. I want to have an isolated resistance, perhaps even a cascade resistance?
no inductance or voltage accepted no extra ohms no volts no amps no NOTHING JUST OHMS. 1megaohm IN 1megaohm out.......????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????

 

[Roff]

You come here asking for a replacement for your relay.
I tell you how to do it.
You think you know better.
I'm done.

 

[crosslakeguy]

No not the case Ron, sorry if I offended..... It is a two part question? 1) I would like a "better design" than I have, something different than what I have?
2)If this design is the only way to make it work, then make it better........ which you have helped on! , the problem I have is i have tried a 4066 It may have been a cd4066, ......I could not make the resistance carry through the IC .I am trying to determine if It works, not a bias between ground, or positive, but a true isolated resistance. I don't know better or I would NOT ask......... I thank you for your help, and only ask that you have tried it and it does work? I spent a day trying , and no avail, thats why I am frustrated!and asking? like I said, don't be offended. im frustrated,
thanks steve

 

[alec_t]

Any switch will have some resistance. None is true zero Ohms.
Why are you so concerned about switch resistance? You can always compensate for that by reducing RA slightly.

 

[Roff]

OK, I guess I misinterpreted your post #11. I will give you a couple of design options, but you first have to tell me the actual frequency ranges you need. I have asked you several times.

 

[crosslakeguy]

I am not concerned with the switch resistance, I am looking at a pass through resistance, If you look at #1 (RB) the sole function of the relay is to introduce a resistance into the circuit, after banging my head, and torturing some of you here, I belive I have come to a resolution to my problem. a DIGITAL POTENTIOMETER. I just looked at a non-volatile digital pot made by XICOR X9C102P, x9c103p, x9c104p or x9c503p. I neen a dual speed switchable pulse generator. low to high, adjustable on low end on the fly. adjustable high, for setup. Ron suggested using the 4066 for this, which I tested and could not get to work on a 1k resistor. so I I still dont know if I made a mistake in my test or there is a misunderstanding on the function of the relay itself? the circuit I have does work as described, I am just thinking there has to be an IC that does this simply

 

[crosslakeguy]

thanks Ron, I will get back at you later, I have to go to work, but will post the values when I can.......

 

[crosslakeguy]

any thoughts on a digital pot? or a 4066 for a resistor array? or a decade up/down counter in cojunction with a 555? and a mystery IC? thought I am more interested in theory than actual values/\/\/\/\/\/\_l---l__l___l____l_____l

 

[crosslakeguy]

I responded via personal message, because no-else seems to know?

 

[alec_t]

Here's how you could use a 4066 to get two independent oscillator frequency ranges. U2a and U2b selectively connect either of two resistor combinations (each a fixed resistor plus a trimmer) to the 555. Additional ranges could be added by using more 4066's/trimmers. Note U2c is wired unconventionally here to form an inverter for the control input pulse (a 0-5V signal).