The first sketch.

01. Conductive top edge

Updated on March 6, 2014.



The Elektrobiblioteka project (V) seems to represent a rather demanding approach, as far as I can make out. The conductive circuits have to be custom-printed on each page, which represents a significant typographical intrusion (unless transparent ink is used) and it is not clear to me how it scales with the number of pages in the book.

The conductive top edge (III), on the other hand, appears conceptually quite elegant and undemanding in terms of materials. It was thus chosen for CB01, the first sketch.

The first step was to verify that the resistance of patches of conductive paint in the shapes of different-width top edges would indeed vary with the width. The paint used was BarePaint, a cheap, commonly available conductive paint based on graphite.

Next, a book textblock was made using adhesive binding with three reinforcement threads. The paper stock was very heavy (230 g/m2) in order to get thick pages which would each make a noticeable difference in terms of the width of the top edge.

The textblock was cut, rounded and backed in the conventional way, and then the top edge was sanded carefully to make it as even as possible.

One coat of BarePaint was applied to the top edge. The paint was undiluted and rather viscous, yielding a relatively thick coat.

A headband was stitched from conductive thread and attached to the back in connection with the painted top edge.

It was now time to test the idea in practice. The textblock was fixed on a board such that the first page touched a metal contact on the board. The resistance between the contact and the headband was measured as the textblock was opened to different pages.

The results showed very clearly that this sketch lacked consistency: the resistance value measured when opening to a particular page varied across orders of magnitude between measurements.

What is more, the value varied also during a measurement, depending on the opening angle and on the amount of pressure applied from above.

I think the main source of this variation is the point of contact between the first page and the metal contact. The amount of pressure obviously influences how well the contact connects with the page; I suppose the opening angle also affects downwards pressure on the contact.

The amounts of resistance between individual pages may also be a factor. Since the coat of paint is rather thick and sits on the outside edges of the pages rather than being absorbed into the edges, minute differences in the distances between pages as well as their relative positions could have notable effects on the resistance of the top edge surface.

One possible conclusion is thus to try and reduce the variation. The most obvious measures would then be to improve the connection between contact and top edge – perhaps by measuring on the first page itself – and to improve the connections between pages – one idea here could be to dilute the paint to the point where it is absorbed into the edges of the pages, then apply several coats; another idea could be to switch to more conductive paint such as a copper- or silver-based one.

Next: A new direction appears.