Characteristics of HP-IL Transformers?

[J-F Garnier]

(09-03-2020 11:14 AM)Martin Hepperle Wrote:  I would not want to recreate a HP-41/71/75 internal HP-IL module, but would like to have a interface building block (hard- and firmware) for microprocessors similar to what the original combination with the HP-IL chip offered.
Similar to the PIL-box but with HP-IL frame de/encoding in the same hard/firmware so that no extra laptop or Arduino etc. is needed. Maybe with an ESP32 or similar device.

The input path uses two transformers in cascade, this was designed in this way for the ESD protection.
If you plan to use pulse transformers with something else than the HP 1LB3 (and later versions), you can use only a single transformer for each input/output path. I would not recommend to change the design for the 1LB3 because the chip ESD protection is special and may depend on the original arrangement (although early HP products/prototypes used discrete pulse transformers, see here for instance).

With the two transformers in cascade (input path), the effective inductance from the HP-IL side is reduced by a factor of ~2 and is about the same as the inductance (also from HP-IL side) of the output path (~2.5mH). So you can take the output transformer characteristics as a model.

J-F