Technical information

a pull-up resistor. When left unconnected the SRF04 behaves exactly as it always has and
is described above. When the "do not connect" pin is connected to ground (0v), the
timing is changed slightly to allow the SRF04 to work with the slower controllers such as
the Picaxe. The SRF04's "do not connect" pin now acts as a timing control. This pin is
pulled high by default and when left unconnected, the timing remains exactly as
before. With the timing pin pulled low (grounded) a 300uS delay is added between the
end of the trigger pulse and transmitting the sonic burst. Since the echo output is not
raised until the burst is completed, there is no change to the range timing, but the 300uS
delay gives the Picaxe time to sort out which pin to look at and start doing so. The new
code has shipped in all SRF04's since the end of April 2003. The new code is also useful
when connecting the SRF04 to the slower Stamps such as the BS2. Although the SRF04
works with the BS2, the echo line needs to be connected to the lower numbered input
pins. This is because the Stamps take progressively longer to look at the higher numbered
pins and can miss the rising edge of the echo signal. In this case you can connect the "do
not connect" pin to ground and give it an extra 300uS to get there.