Question for RG and some comments concerning cd4017

[donald stringer]

I have a project that I am going to be posting in the gallery soon.I am making the box now and finishing the design for the perfboard layout. I am using one gate of a cd4093 and a momentary switch to debounce  pin 14 of a cd4017. ok I made it count to four on the bread board no problem. In my limited knowledge the 4017 likes to light leds. I am using three cd4053 for a three effects loop box with bypass according to your design and that works well. I am going to include no. 4 just to light an led for now for possible future expansion. As I was studying for this project [googling for varieties of 4017 circuits] all that I came across were using the output of the 4017 to light leds in many configuration and I understand that but also came acsoss many that were using the outputs to drive the contacts of an 4066 etc..... Question #1 does it take less output to drive the contact of a 4066 bilateral [I am using the quad seq. switcher as my point of ref.] as the schematic clearly shows the cd4017 driving the contacts and using an transistor to light led ? What I have discovered  is the 4017 WILL NOT drive the contact of an cd4053 ...yes I had to go back and read again that it requires 6 volts for a logic high and 3 volts for low. I went back to the breadboard and put a trans. in line  between the output of the 4017 and the contacts of the 4053 and now it works. I just automatically assumed that the 4017 would drive anything , a learning experience for me anyway...Question#2 can I use the third spdt to light an led [9, 10, 11 effect on, led lit] and how would I accomplish this ? Third and last as for my comment as I went a googling and breadboarding there are a lot of schem. in error, do designers get some kind of insane enjoyment out of posting erroneous inf. I mean if I were an electronics designer and posted an schem. on my site for all of cyberspace to view at least I would go to the trouble of making sure it works first. If it were that secritive keep it off the net. But  that is also our resp. to acquire correct input to make sure we know the difference. One small example I went through three res cap. momentary switch combinations to operate the cd4093  before I finally pulled one off the net at random and it worked [this one I am staying with]  O K as for my previous rambling   present company discluded, and anyway what do I know this is suppose to be my relaxing hobby and for me personally it is somewhat of a learning curve to absorb. Thanks for your thoughts comments suggestions into this project and anything cmos.

[bioroids]

I think the 4017 can drive the control input of the 4053, it should not need a transistor buffer. At least if you have the same Vcc (say 9v) in both, the high and low levels are the same for both circuits as far as I know. And it should take no current, because the 4053 control inputs ar CMOS. Am I wrong?

On the other hand, driving the led takes at least 1ma of current (depending on your voltage and the led resistor) wich I also think the 4017 out can handle (at Vcc=9v). But if you need more current is better to use a transistor there.

Hope this helps

Miguel

[gez]

4017 outputs are within a gnat's gonad of the supply rails.  There should be no problem with switching other CMOS chips, unless you're running them at different voltages?

PS  How were you connecting them up?  Were you draping LEDs off the outputs and connecting the junction of the LED and current limiting resistor to the switches?  If so, try direct coupling from the 4017 outputs.

[donald stringer]

Hey gez, The cd4093 debounces the 4017 [wired for a four output count 3247]. Those four outputs connected [via] short jumper wires to an radio shack 10 segment led with the neg. side of  the led to ground through an 3.3resistor. This setup causes it to count 0,1, 2,3 as it should. The next step was trying to connect the first output to the contact of the 4053 only [ with no led] ....nothing. Everything has 9 volts by the way. The 4053 wouldnt switch without the transistor in line. So I tried direct coupling this didnt work without the transistor.

[R.G.]

We need some Datasheet Reading 101 here.

The CD4017 is a CMOS logic output device. That is, its outputs can only be one of two states - pulling up and pulling down. There is no middle with the chip's outputs.

CMOS outputs look like small resistances to the power supplies (either Vdd or ground) when they are in the high (Vdd) or low (ground) states. Because they look like resistors, they cannot supply large currents, and the more you load them down, the less perfect the output goes.

I think you were driving LEDs directly from the CD4017 output. That works because the CD4017 datasheet says that the 4017 working from a 10V power supply can source as much as 0.9ma to a load and still pull it up to 9.5V. So the output looks like a resistor of 10-9.5v/0.9ma = 555 ohms. If you put an LED to ground there, the 4017 would pull the LED up to its normal 2V but that's all, because it can't supply any more current. If you measure the LED voltage when the 4017 is on and off, you'd find that the voltage is either about 2V or 0.

The 4053 selector inputs expect a logic signal on their input. The spec sheets says anything over 6V will be treated as a logic 1, and under 3V as a logic 0. With the LED holding the 4017 output under 3V, the 4053 thinks it's always getting a "0", albeit a sloppy one. So no, the 4053 won't switch.

If you put a resistor to the base of a transistor from the 4017, now the 4017 sees only the resistor/base as a load, and if that's high enough resistance/low enough current, then the CD4017 output will switch from nearly 0V to nearly 9V. And the transistor collector will switch from open to a short to ground. If you put an LED in the voltage-to-collector path, the transistor will try to burn up the LED or the transistor. You need a limiting resistor in series with the LED. Then the transistor will turn the LED on and off. And also the CD4053 can be driven from the output of the CD4017 and get a good logic signal.

You're overloading the cd4017 outputs. Goes-inta-s has to match goes-outa-s.

[donald stringer]

Thank you so much for clearing that up for me. I will have to go back and try it again.