Hi can someone put us straight on this.
Can you directly connect an out put of a 4000 series chip to the "reset" of another 4000 series chip and expect it to last ??
Sounds pretty basic, but the reason I ask is this..
I was happily connecting up good ol 4017's and using a nand gate's output (4081) to reset them. (Running 12 Volts and a 1Hz clock cycle) I started to measure and, noted that my Fluke 73III was not seeing any activity on the reset line, yet the chips were all resetting when they should and everything was working as it should.
I connected up my old Trio 40Mhz scope, still nothing on the reset line!
So I measured the resistance to earth.... 109 Ohms.. on every "reset pin" of the 4017's.. ( I was using a 100K resistor to tie the 4017's "reset pin" to ground ).. Now if that 109 Ohm resistance is right, then that will mean about 110mA at 12 Volts.
Since these chips are only supposed to deliver (on red-line) 10mA absolute max, I think I was experiencing voltage sage from the nand gate's output.
I see many circuits online where the output port of a 4000 series chip directly connects to a reset pin, but if you want your circuit to last a fair few years, is this really the best practice? Will these directly connected chips last the distance ??
Or should we jam in a 1.5K "series" resistance to limit the current to about 8mA.at 12V??.
Many thanks for your time guys...