Multiple Baby 8's on One Clock

d3adpix3ls · Joined: Jul 16, 2019 Posts: 2 Location: United States

to preface, i'm just a dude with a soldering iron, and a passing interest in electronic music. most of the time its just me blindly fumbling about until something works. so yeah, built a couple of baby 8's paired with dual 555 apcs. thought they were interesting but i wanted more. specifically polyphony. so i built a larger rig split into 2 banks of 3 sequencers, 3 apcs, and 3 wsg filters. picked up a couple 3-tiered rotary dials so i could control the step counts for all of the seqs in each bank. was feeling pretty good about it all. then i hit a brick wall with the clock. i mean there's no way a single 555 could handle it right? acting as a trigger for 6 4017s? that was the initial assumption i was operating under. i've seen a few references to using one as a master to trigger others, but. ugh. seriously. i don't know what to do. in too deep to abandon the project at this stage. weeeeeee...

PHOBoS

Actually a standard 555 should be able to trigger 6 4017's easily, and I am pretty sure the CMOS version (which is preferred) can do it too.
That's the nice thing of CMOS chips like the 4017, the inputs have a very high impedance so the current needed to trigger it is very low.
As a result you can drive quite a LOT of inputs with a single output. (for more info on this search for fan-out).

JovianPyx · Posted: Tue Jul 16, 2019 4:58 pm Post subject:

This is a question of fan-out.

Looking at 40106 as an example, output current is no higher than 8.8 mA. Input current is around 1 uA. so from that we can guess that it should easilly drive 50 or even 100 CMOS inputs.

The 555 is bipolar TTL and has huge fanout into CMOS, so yes, it could drive the whole network.

7555 is CMOS (there are also other numbers for CMOS 555) and has less drive capability than the bipolar 555.

The 7555 datasheet I have says around 20mA source (best case), but less than 1mA sink (best case), so I would connect it's pin 3 to a 40106 and let the 40106 drive the network.

d3adpix3ls · Joined: Jul 16, 2019 Posts: 2 Location: United States

again. dude with a soldering iron. so i'm overthinking it for whatever reason and a single 555 can handle the load? if that's the case, i have pissed away so many hours...

ixtern · Joined: Jun 25, 2018 Posts: 145 Location: Poland

In CMOS world input capacity is more important than input current (unless we are talking about static levels). If you want to drive multiple CMOS circuits and not to lost signal shape, low impedance output is required. All depends on specific circuit. 555 is specified for output currents up to 200mA. 7555 can drive 2 standard TTL loads (datasheet) (Isink max depends on voltage).
For 555 - open collector and for 7555 - open drain outputs may be also used with external resistors.