Re: LOTS of US Water Plants Hit by Hacks

On Tue, 4 Aug 2026 11:14:58 +0100, The Natural Philosopher wrote:

> On 04/08/2026 08:10, rbowman wrote:
>> On Mon, 3 Aug 2026 20:50:24 -0400, c186282 wrote:
>> 
>>>     Anyway, hardware PLCs are pretty stupid - you don't actually hack
>>>     them directly. They're basically a replacement for a box of relays
>>>     or equivs. Software PLCs - a uC or even better - are more
>>>     "computers", oft net-connected these days. An Ard Uno would make a
>>>     fair software PLC. A low-end PI even better.
>> 
>> https://www.realpars.com/blog/plc-hardware
>> 
>> What's a hardware PLC? It amazed me to find that they still use the
>> ladder logic metaphor. I thought that was a temporary crutch when they
>> started showing up in the '70s.
>> 
> I would assume its a chip with inputs , outputs, containing a
> programmable state table
> 
> So a state machine in silly con.

Relay logic always was very much a state machine. When the moving part 
hits the limit switch, transition to the next state.

https://www.plctalk.net/forums/threads/eagle-signal-mta330a6-05-what-kind-
of-plc-or-control-is-this.129042/

Steppers made it very obvious. An input, be it a timer, limit switch, or 
pushbutton, would advance the drum one step. The solenoid had a very large 
lead counterbalance that made a pleasing 'thunk'. No question about a 
state change. Nubs on the cams determined which outputs were live for 
every step.

The earlier Eagle Signal steppers required breaking out a tab on the cam 
with needle nose pliers. Revising the programming required disassembling 
the whole thing to replace the cam. Later some genius redesigned the cams 
with removable nibs that snapped on the cam.

In the '70s the company I worked for built the controllers used for the 
sequenced airport landing lights (rabbit). The FAA, being rather slow 
moving, specified steppers with the wiring harness being laced rather than 
using those new fangled nylon TyWraps.  Fortunately the girls, excuse me, 
female electronics technicians, were skilled in macrame.