07/05/2026 · 5 min read
I spent longer than I’d like to admit scrolling through eBay listings trying to work out which Siemens S7-1200 to buy. There are numerous variants and trip hazards that, as someone who’s not an automation engineer, caught me out a lot.
Now that I’ve picked up my own 1212C DC/DC/DC from eBay, this guide is what I wish I’d had when I began my search.
Every S7-1200 has a part number that tells you everything you need to know - if you know how to read it. Here’s how to decode it.
Take 6ES7214-1AG40-0XB0 as an example:
| Segment | What it means |
|---|---|
6ES7 |
Siemens SIMATIC S7 family |
214 |
CPU model - 1211, 1212, 1214, or 1215 |
1 |
S7-1200 subfamily indicator |
A / B / H |
Power input - A = DC, B = AC, H = DC (relay DO) |
G / E |
Hardware revision |
40 |
Firmware generation - 40 = V4.x (current), 31 = V3.x (older) |
0XB0 |
Hardware revision suffix |
For example, my PLC had the model number ‘6ES7 212-1AE40-0XB0’, which means it’s an S7 1212 with a DC power input and version 4 firmware.
As well as the model name, you might also see DC/DC/DC or AC/DC/RLY. The first part of this notation indicates the power input type, the third part indicates the digital output type. Read on to learn more!
Full model table from Siemens.
There are four common CPU models of S7-1200 PLCs you’ll see online. For a hobby or learning rig, the differences come down to onboard I/O count. The main difference is the I/O - the number of Digital Inputs (DI), Digital Outputs (DO, or DQ as Siemens call it), Analogue Inputs (AI), and PROFINET (or Ethernet) ports.
| CPU | DI | DO | AI | Ethernet Ports | Notes |
|---|---|---|---|---|---|
1211C |
6 | 4 | 2 | 1 | Enough for basic automation and learning. |
1212C |
8 | 6 | 2 | 1 | Enough for a home lab, plus some head room. |
1214C |
14 | 10 | 2 | 1 | Nice to have extra I/O, but comes at a higher price point. |
1215C |
14 | 10 | 2 | 2 | Same I/O as 1214C but adds a second Ethernet port. |
For most, the 1211C or 1212C should be enough I/O if you’re just using it as a demo or research rig. It could be worth upgrading to the 1215C for the second Ethernet port but you’ll pay a premium to do so.
The PLC come in two different power input types - DC and AC.
A DC unit can be powered by a 24VDC Power Supply Unit (PSU) - likely what you’d want if you’re planning on using a 24VDC DIN rail mounted PSU.
The AC unit requires mains, 100-240VAC. Be careful when scouring eBay, the AC units are often cheaper but may not be what you want.
The third part of the DC/DC/DC notation is the output type. This matters if you want to do anything interesting with the outputs beyond simple on/off switching.
The S7-1200 is an excellent platform for hands-on learning - Modbus TCP, OPC-UA, S7comm, and PROFINET all in one box, programmable with TIA Portal software. The used market is active enough that a good unit comes up regularly - and if you’re willing to wait, you can snag a good deal.
The key is knowing what you’re looking at before you bid. Decode the part number, check the seller feedback, and don’t pay 1214C prices for a 1212C just because the listing title says “S7-1200.”