HP 15

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This patent seems to describe this cartridge. It expires in June 2018 in case there was ever any issue due to reading it.

Basic Principles

HP 15 is a thermo cartridge. It has a matrix of nozzles, each consisting of a heat resistor. When current is allowed into a resistor, the resistor heats up, making some of the ink in its nozzle evaporate—as a gas the ink expands its volume, creating overpressure and ejecting a drop of the remaining liquid ink.

Now, the first ink cartridges had only a small number of nozzles (e.g., 14) and each resistor was connected to a contact pad. To keep the number of contact pads low while taking the number of nozzles one order of magnitude higher, cartridges organise nozzles in a matrix. A current needs to be applied to a ``column pad'' and a ``row pad'' to actually activate a nozzle.

Cartridge Pinout

Source: the patent above.

(Please note: what I call here ``pins'' are actually contact pads on the cartridge.)

Pin Matrix

474951   525048
414345   464442
353739   403836
293133   343230
2527   2826
2123   2422
1719   2018
1315   1614
911   1210
57   86
13   42

Pin Meaning

1A9Address Select 9
2G6Common 6
3PS7Primitive Select 7
4PS6Primitive Select 6
5G7Common 7
6A11Address Select 11
7PS5Primitive Select 5
8A13Address Select 13
9G5Common 5
10G4Common 4
11G3Common 3
12PS4Primitive Select 4
13PS3Primitive Select 3
14A15Address Select 15
15A7Address Select 7
16A17Address Select 17
17A5Address Select 5
18G2Common 2
19G1Common 1
20PS2Primitive Select 2
21PS1Primitive Select 1
22A19Address Select 19
23A3Address Select 3
24A21Address Select 21
25A1Address Select 1
26A22Address Select 22
27TSRThermal Sense*
28R10X10X Resistor*
29A2Address Select 2
30A20Address Select 20
31A4Address Select 4
32PS14Primitive Select 14
33PS13Primitive Select 13
34G14Common 14
35G13Common 13
36A18Address Select 18
37A6Address Select 6
38A16Address Select 16
39A8Address Select 8
40PS12Primitive Select 12
41PS11Primitive Select 11
42G12Common 12
43G11Common 11
44G10Common 10
45A10Address Select 10
46PS10Primitive Select 10
47A12Address Select 12
48G8Common 8
49PS9Primitive Select 9
50PS8Primitive Select 8
51G9Common 9
52A14Address Select 14

*) I suppose these two pins take care of the ink temperature (both measuring and heating), but I have not found any (patent-) documentation to back this up. What I have found out, on the other hand, is that the HP printer is very sensitive to any outer interference on them. For instance it may think that the ink is not yet heated to the target temperature so it waits and waits and waits… and prints each pass of the printing head with long intervals as a result.

Note: not every combination of an address select and a primitive select is connected to a nozzle. I actually don’t know yet, but I’ve read elsewhere that there still might be resistors present – those would be used for maintaining ink temperature. But that was a general idea on thermal cartridges, not HP 15-specific information. Another theory is that they can be used to encode cartridge identification bits. (To do: investigate this.)

Nozzle Matrix

To do: manually transcribe it here from the PDF.

Experimental Voltage Measurements

To do: create a schema of the measurement circuit and type up my notes here.

Last updated: 2018-03-03