How to choose a microcontroller?

[charlesli]

I've been thinking about a project recently about car charging stations.
I want to apply the RFID principle to achieve swipe card charging.
So how do I choose a microcontroller?

 

[rjenkinsgb]

Just about any that can handle serial data and has at least a couple of hundred bytes of RAM (not actually essential, but it makes it simpler) - a PIC, arduino, raspberry pi, just about anything...

A typical RFID reader interface just sends a stream of serial data; either conventional serial, or wiegand format - two data wires, pulsed for one and zero bits respectively.

You wait for a full card number to be received, then compare it to the list of valid cards stored in the device memory.

Or for a card that contains "credits" you need a Mifare style card and reader/writer.
That gives you the card number, but also allows data to be read and written securely, you you can check a credit count and write back one less to "pay" for a service.

This is an example ready built Mifare reader/writer with a serial interface:

ACR122S - Serial Interface NFC Reader/Writer

NFC reader/writer with RS-232 serial port. It can read and encode NFC Tags type ISO14443 A and B, MIFARE, Felica, NFC Forum types 1-4. This product is out of production. Alternatively, we recommend the NFC reader ACR1281S-C1.

www.shopnfc.com

Or you can get a module such as this, with a matching antenna, and build your own device:

Eccel Technology Ltd RWD-MICODE RFID Module 13.56MHz, 5V | RS

uk.rs-online.com

Eccel Technology Ltd ANT1356M (000144) Antenna, High Frequency RFID | RS

uk.rs-online.com

Look at the data sheet link in the module listing for the technical info.

 

[charlesli]

That's great! I was initially thinking of paying by coin and then using a regular MFRC522, but it's great to hear you say that there is a module that can read credit cards and the ability to make payments.

 

[rjenkinsgb]

that there is a module that can read credit cards and the ability to make payments.

To clarify, not "Credit cards" as in bank cards, but cards with writable memory that allow you to create a token payment system, so you can "top up" a card and then subtract units as it is used.

 

[Pommie]

Have you looked at square terminals?

Mike.

 

[charlesli]

To clarify, not "Credit cards" as in bank cards, but cards with writable memory that allow you to create a token payment system, so you can "top up" a card and then subtract units as it is used.

Maybe you have a link to Amazon?

 

[charlesli]

Have you looked at square terminals?

Mike.

What is a square terminal?

 

[Nigel Goodwin]

What is a square terminal?

It's like a round one, but with straighter sides

Honestly? - I've no idea either.

But a simple google does:

Square Terminal | Square Shop

Square Terminal is your all-in-one device for payments and receipts. Take every type of payment quickly and securely.

squareup.com

 

[Pommie]

What is a square terminal?

One of the things they appear to produce is a terminal that can be incorporated into other products.

Mike.

 

[charlesli]

One more question guys, how do I implement this charging process?

 

[Nigel Goodwin]

One more question guys, how do I implement this charging process?

By researching all the requirements (which 'could' involve large fees to access - who knows), and then designing a system to meet those requirements.

 

[rjenkinsgb]

how do I implement this charging process

There are two approaches:

For stand-alone units (no internet connection), you need to create an encryption key and use that when writing data to the card.
You load or charge it by reading the credit value stored in the encrypted data, and adding however much the user pays for.

The target device works in a similar way, reading the data using its key and subtracting the cost of the service being paid for.

Read the Mifare interface documentation in detail - that has info on reading and writing data and the encryption keys.
"Your" service must have its own unique encryption key, so no device without that can change the data on the card relating to your credit system.

If everything is internet connected, you can have the "credit" data stored in user accounts on a web server and top up via such as paypal.
The target device units just need to access the web server to check and update the credit for that user ID.

 

[charlesli]

Maybe I didn't express myself clearly, I was asking how to achieve charging (electricity)? Do I need a battery pack or something to make it happen?

 

[rjenkinsgb]

Maybe I didn't express myself clearly, I was asking how to achieve charging (electricity)? Do I need a battery pack or something to make it happen?

Start again and give fully detailed info on what you mean?

Your first post related to CAR charging stations. The commonest type electric car charge devices (usually with Type 2 connectors now) just feed mains AC to the vehicle connector, with some monitoring and control so power is not switched on until the connector is in place, plus it also "tells" the car system the maximum current it can supply via a PWM signal on the CP pin. Plus safety devices such as an appropriate ELCB etc.

All the charge control and battery monitoring etc. are done within the vehicle electronics.

Charging station - Wikipedia

en.wikipedia.org

There is also another data transfer system possible on the CP pin for two-way communications if the charge unit and vehicle support it, so eg. the vehicle ID can be passed to the charger for automated billing, the "Plug and charge" system.

ISO 15118 - Wikipedia

en.wikipedia.org