GY401 to 9251/9256 or BLS251 Adapter
I designed this unit to sit between the GY401's output and the tail servo. The unit simply converts from a 1.52ms to a 760us centered pulse stream, with an output frame rate fixed at 333Hz.
The converter does not expect any particular input frame rate so could be used with many other gyros that support standard pulse width servos.
The unit also provides a means to set each travel end point for the tail servo, a feature missing from the GY401 (it only has the facility to either increase or decrease the overall travel, so with asymmetric tail setups one direction often doesn't get the maximum throw that it might otherwise achieve).
Setup mode is entered by powering up the device with the push button held down. Maximum mechanical end points can now be located by using the rudder input in combination with the push button. As the rudder stick is operated, the servo will slowly advance or retreat in the particular stick direction, with centre stick causing it to halt at its current position. The software will force you to set each end point independently. Once a given limit has been found operating the push button will store it permanently. After the second end point has been stored the unit exits setup mode and begins operating normally.
If during flight the unit suffers a brown-out it will flash the LED, or if the unit is reset as the result of a software problem the LED will illuminate permanently, this second type of reset should never occur! Errors are persisted across power cycles and must be cleared by operating the push button.
The unit is based on the 16F628A PIC microprocessor and the software has been developed in assembler using the free MPLAB development IDE from Microchip. The complete assembler source and MPLAB project files are available here: MPLAB_Project.zip
In circuit programming is achieved via ISCP header (4 pin SIL connector on top left of the PCB). Power from the programmer is also required and needs to be supplied to the unit via either the servo or gyro plug.
A full parts list is available here: parts list
The Gerber files required to fabricate the PCB are available here: Gerber_247_Files.zip
