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medical equipment for developing countries

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 jPNSThe jfish PeripheralNerve Stimulator.

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To design, build andshare a range of open-sourceanaesthetic

monitoring devices.Unencumbered byintellectual property

 

Trace: Home » devices » devices:jpns » workings

The jfish Peripheral Nerve Stimulator

About Specs How Build Use

How does the jfish PNS work?

The jfish PNS circuit is made up of three core parts:

.1 A digital stage comprising a small microcontroller (currently a PICAXE08)running the open-sourced embedded firmware, and serving as the ‘brains’of the device. The microncontroller controls the pulse patterns, by sensinginput from the four user-buttons and responding with output gating of thehigh voltage stage.

.2 A high voltage analogue stage consisting of a step-up DC-DC converter controlled by a Maxim MAX642 IC. This stage steps up the battery-supplied 9V to the 300V required for maximum current output. TheMAX642 uses a small inductor and fast-switching Schottky diodes to

store charge from the 9V supply..3 A current mirror that ‘mirrors’ the potentiometer-selected current to the

output electrodes regardless of the patient’s skin impedance. The outputvoltage is thus automatically presented by the current mirror, determinedby the relationship between the user-selected output current and the skinimpedance.

Several other features are implemented as part of these three core components:

Battery voltage check provided by the MAX642 IC.LED and piezzo buzzer output to indicate pulse delivery, controlled by themicrocontroller outputs.

Low-power mode, switching off the high voltage stage, controlled by themicrocontroller.

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 protected fromcommercialexploitation.

Appropriate for usein developingcountry anaestheticsettings.

Modular in designand readilymodifiable for localneeds.

Supported byextensive freedocumentation.

To establish a non-profit foundation tosupport the projectgoals and distribute jfish technology.

To fosterempowerment andencourageinnovation inmedical communities

in the developingworld.

Logged in as: Daniel Jolley devices/jpns/workings.txt · Last modified: 2005/09/24 21:16 by djEdit this page Old revisions Admin Logout

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 jPNS Schematic

The jPNS schematic is relatively simple. The three core stages outlined in theflowchart can be readily identified. (Clicking on the schematic will open a full-sizedversion.)

A detailed description of the schematic can be found in the   jPNS Design Notes.The PNS change log also contains further description of aspects of the circuit,particularly as these relate to improvements and evolution of the design over time.Both these documents are kept within the project document repository.