A student builds an mbed-based system. To one port he connects the circuit of Fig. 3.17A, using

Question:

A student builds an mbed-based system. To one port he connects the circuit of Fig. 3.17A, using LEDs of the type used in Fig. 3.4, but is then disappointed that the LEDs do not appear to light when expected. Explain why this is so and suggest a way of changing the circuit to give the required behavior.

Fig. 3.17A