Originally Posted by: TEEPOL 
I have 13 old analogic locos bougt in the 70's, working very well and I am thinking about transfering my net to the digital.
I am just begining to buy secund hand digital locos and I plan to share my network in 2 : Analogic and digital.
First of all I am wondering what kind of central unit 6020 : 6021 : 6035 ...or Mobile station CS 2 / CS 3 to buy.
I am lost with the different models and how it is connected to each other
I plan to have 2 or 3 locos with sound but it is my priority.
Have you any documentation to understand what kind of station to buy and the different parts of the puzzle ? (secund hand preferred for cost reasons)
Thanks for the help
Hi TEEPOL (Un prénom serait super)
First it is great to have you with us. A warm welcome to this great forum.
Here a Märklin fan from Ile de France, started in 1961 with M track, a loop of rails and a 3037 (E41 loco) and now with a permanent layout with digital and PC control (Rocrail
Here is a glimpse of my present layout with C track, if you are courious
https://www.youtube.com/watch?v=F6WnhXPcRqIWhat kind of Central Station?- I used a 6020 (the very first Central Unit), then 6021 (with MM2 protocol), then CS1 60212, then CS2 and now CS3
- 6021 was really a good unit, mine is still working but now quite outdated
- CS1 was a scam by ESU resulting with a legal fight between ESU and Märklin, so poor unit, poor display, no update no maintenance
- CS2 was an excellent unit (60215) provided you avoid early units 60213 and 60214 which had a design problem (no galvanic separation. Only one drawback: they are not maintained by anyone (so when it fails, it goes to trash)
- CS3 is very good but expensive (I purchased mine in Germany like 2 years ago for approx. 580€).
Just a suggestion here but why not starting with a digital stater kit (I just bought a 29243) or a Mobile station 2 with its trackbox 60116 and its 36 W power supply.
It will allow you to taste digital before making large investments. Drawback you give up the possibility of feed-back signalling
Connection to digital modules- locos need to be digital or upgraded using digital kits mostly for DC motors mLD3 low cost), mSD3 (sound) or for old Märklin locos with "universal" motors (winded inductor)
- switches or signals could be analogue (regular wiring totally separated from the digital part) or digital using either a 4-way decoder M83 (60832) or imbedded decoders 74462 (more expensive but great for carpet trains and not good for permanent layouts). Avoid using 6083 modules (cheap but no safeguard to turn the solenoids off)
- detection is only applicable with central stations (6021, 60212,60213-60216, 60226). It uses the S88 family (now 60881, 60882 (for DC), 60883 (Link 88 (required with CS2s or CS3 (60226). Avoid using older generation of S88 (6088, 60880) with its flat cables, prone to bad contacts and electric interferences.
Digital and analog together?- If, by accident, digital power is connected to analogue power, the risk of destruction is really big
- so the best is to have 2 independant zones, one for analogue, another for digital without any connecting track inbetween.
- another possibility is to install a switch to feed your layout EITHER with digital or with analog power.
So looking forward to read from you and your projects
Cheers / Amicalement
Jean