Reusable physical coins using the bitcoin network | 2022

//  The main concept

Reusable physical coins using the bitcoin network

Draft - Beta version 0.1.1


We propose an alternative to the known wallets, a reusable physical coin that
uses the bitcoin network but functions like cash. 

The coin allows both electronic and physical transactions.

These physical coins contain the public and private keys, thus making bitcoin 
a true alternative to the payments ecosystem by slowly replacing fiat.

We know there is a plethora of wallets but we propose a way to keep custody of
coins in the simplest possible way while being able to transmit those coins 
physically as well, without the need to broadcast the transaction.

This document assumes the reader understands how bitcoin works, how transactions
are confirmed and how cryptography secures the whole network and the individual 


The physical coins store the private key in its binary form in a 16 by 16 mesh
that uses a close circuit that converts the associated private key to the 
corresponding public key where funds can be sent.

All is done offline, and it is powered by solar energy (a small lithium battery
can be installed if desired). 

In this first version (0.1) we use the legacy addresses of the type 1A1z… and 
each coin may contain whatever amount we desire, there are no denominations. 

It is both a cold wallet for storage and a functional wallet that allows 
sweeping the private key into any app to transact with any peer.

Traditional hardware wallets require the use of apps to interact with them and
some make it very complex or even virtually impossible for the average user 
to safely store and use their coins.

Our proposal is an alternative to the existing universe of wallets for those 
who may see the physical delivery of coins as a plausible feature. 

We made the verification of funds so trivial that the average citizen can 
relate to cash easily.


The Casascius coins are a very interesting precedent, but the process used 
to mint them implied trusting that the issuer did not store the corresponding 
private keys and that he used enough entropy to generate them. 

So far, it has been proved that he was honest, and his project will always 
be remembered as an important milestone in bitcoin’s adoption history.

Our proposal removes trust completely since the private key is not previously

Our reusable coin is a blank canvas at the very beginning and can be reset as 
many times as needed. 

If the coin has been already used previously a simple reset and corresponding 
generation of a new private key is very easy and intuitive. 

The general precautions when generating the private key must be followed, 
especially avoiding someone peeking at it during the process. 

Once generated it will be safe if the rest of the instructions are carefully 


The fig x. shows a thin metal plate that consists of 256 holes that will 
let us create a binary private key using true randomness. 

The coin does not connect to the internet, the only way to verify they contain
the appropriate private key for the public key — bitcoin address — is by 
following the instructions and sweeping the private key that will let the 
user verify that signing a transaction is possible.

To check the balance is enough to scan the QR generated by the coin itself
(the public bitcoin address) using the integrated circuit shown in fig. x and 
connecting to some explorer or node who is able to reveal the balance or the 
outstanding unspent transaction outputs (UTXOs).


The crucial aspect of these coins is the ability to easily check the balance 
and that the coin itself contains the private key and there has been no 
tampering at all. 

In order to provide this level of security, we need to establish different 
levels of use.

a) User that is storing coins as savings (cold storage).

b) User that wants to receive them physically.
In this case, whoever receives the coin needs to verify not only that the 
address has the corresponding funds but also the associated private key to 
move them in case it is needed or for extra peace of mind in case there is 
suspicion that the previous owner may have had access to the private key.

It is highly recommended to move to another address by sweeping the private key 
into a hot wallet and then resetting the coin to a fresh new address of your 
choice by following the instructions.

Other cases. (pending review - May 2023)

//  The components

To create an integrated circuit (IC) that converts binary into hexadecimal, 
I would start by defining the input and output requirements. In this case, 
the input would be binary numbers, and the output would be the corresponding 
hexadecimal representation.

Next, I would design the conversion logic. I would develop the logic that breaks 
down the binary input into groups of bits and maps each group to its 
hexadecimal equivalent. This logic can involve using various components such 
as logic gates, flip-flops, multiplexers, and decoders, depending on the 
complexity of the design.

Once the conversion logic is designed, I would select the specific integrated 
circuit components needed to implement it. These components play a crucial role 
in executing the conversion algorithm accurately and efficiently.

With the components selected, I would create a schematic that represents the 
conversion logic. Using schematic capture tools or design software, I would 
connect the chosen IC components according to their functionalities and the 
desired conversion algorithm.

To ensure the functionality of the circuit design, I would simulate and test 
it using dedicated software. Through simulation, I could verify that the 
circuit accurately converts binary input to the expected hexadecimal output. 

I would test different binary input values to ensure the conversion is 
consistent and correct.

Once the circuit design is validated through simulation, I would move on to 
creating the physical layout of the integrated circuit. This involves 
arranging the components and their connections to optimize performance and 
minimize signal interference.

The next step is to send the IC layout to a semiconductor foundry or 
fabrication facility for manufacturing. The fabrication process involves 
creating the IC layers, depositing materials, etching, and adding metal layers 
to establish the necessary connections.

After fabrication, the manufactured ICs undergo rigorous testing to ensure 
their proper functioning. Electrical tests are performed to validate the 
conversion accuracy and reliability of the ICs.

Once the ICs pass the testing phase, they are integrated into a package that 
provides physical protection and facilitates connection to external devices or 
circuits. This package can be a ceramic or plastic chip carrier.

Finally, the completed ICs can be integrated into larger systems or electronic 
devices where binary-to-hexadecimal conversion is required. These ICs find 
applications in various domains, from display drivers to microprocessors or 
communication devices.

It's important to note that creating an integrated circuit and going through 
the entire fabrication process requires specialized knowledge in electronics 
and semiconductor manufacturing. The process I described provides a high-level 
overview, but the actual implementation may vary depending on the specific 
project requirements and constraints.

//  The goal

As it has been stated in previous drafts, the idea behind is to facilitate
the offline transmission of bitcoin without broadcasting the transaction.

The physical coin stores a private key that produces an address to send funds
to and that let's keep that as cold storage.

When receiving a coin like this it is recommended to move the balance to a 
new coin which private key we have generated.

The generation of the private key is random.