Re: [Taler] Taler wallet charge terminal

[Christian Grothoff]

On 9/22/23 13:40, Florian Jung via Taler wrote:
> Hi,
>
> I want to build a wallet recharge terminal, i.e. a machine that eats 
> real money banknotes and gives you Taler; for this project, I have a 
> couple of questions:
>
> Does previous work on this exist already?

Yes, there is starting code in the taler-mdb.git and Andreas (in CC) is 
presumably working right now (TM) to hook this up to a coin acceptor. 
Also, Sebastian had done some first prototype with a cash acceptor.

> I know about the Taler snack 
> vending machine, but IIUC, this is the opposite direction (eats taler, 
> gives food). How are people charging their wallet in this setup?

Cashier app + physical cash to real people.

> What bank- or nonbank/nexus setup would be appropriate for such a 
> terminal? 

We're actually planning on using the grant (previously: tip) API from 
the merchant backend. Basically, provision a reserve with the maximum 
amount the cash acceptor is allowed to hand out (until you empty it...) 
and grant from the reserve whenever a user puts in coins.

> Does it make sense to use a libeufin demobank setup where, for 
> every real euro fed into the machine, the "central bank" wires a 
> currency unit to the exchange's demobank account? Or would it be more 
> appropriate to have a "banknote acceptor backend" for the nexus, and 
> skip the demobank completely?

We plan to not interact directly with the bank/nexus at all for this.

> I'm gonna run this with a local currency, but am looking forward to 
> Taler being offered by a real bank someday; in such a future, I would my 
> merchants (all under my control) to support payments both in local 
> currency *and* in euro-taler. I've seen that the contracts v1 protocol 
> supports "alternative contracts".

Right, that's under preparation. I also already updated the merchant 
backend to become more multi-currency capable. Once this is done, you 
should be able to accept different currencies from the same merchant 
backend. Alas, work-in-progress.

> Do I correctly assume that this would allow for "pay in euro only" and 
> "pay in local currency only", but not (easily) allow the user to freely 
> choose the ratio between EUR and LC (i.e. pay 81% by LC but the 
> remaining 19% with euro)? (Though I could offer them a lot of such 
> alternatives, so they could at least choose in steps of 10cent or 
> something)

The idea is that the merchant frontend would basically specify to pay 
*either* 5 EUR *or* 6 CHF *or* 5 CHF plus 20%-off discount coupon. So 
the backend will *not* have a currency conversion ratio, the 'current' 
ratio is for the merchant frontend to know/decide upon.

> Also, what is the current state of NFC support in taler? Can I already 
> use NFC for buying and charging my wallet? What specs would a NFC reader 
> need to fulfil for that?

The current (Android) wallet already supports NFC. If your phone can 
read NFC tags, it should work. On the machine side, you don't need an 
NFC reader, but instead a device that can send NFC tags to the phone.

Happy hacking!

Christian