Very good your Balancing scooter, PaulC.
"My beach" are the Basic and the assembler of MCU´s based on 51 family achitecture.
I've a old hobby: The electric vehicles.
And some days later redesigning the ZZAAG3 PCB's with two separated boards. One for control with a 40 pin (DIL) Atmega32-16. The second with the 2 motor power drivers. The IMU (gyro - IDG500 & accel ADXL325 are a cheap (maade in China) 5 DOF board).
The basis for my personalised PCB layouts are a "gyropode" article published on french magazine Electronique Pratique.
After the AVR firmware programation with the necessary fuse presets, specially the external xtal oscillator, I saw a error: Only the red LED flashing and nothing more... That's the reason I´ve posted the help request here...
Well... With some research on the Bascom AVR and the literature of Elektor Weellie balancing scooter I have discovered the error!!! Baaaaaaaa!!! My attention!...
The E. P. magazine have the bad indication of 5V on the AVR - ARef ( ref. for ADC's ). With 3V the problem remain corrected...