Prototype super easy -
Check out circuit diagrams here
Adding an LCD ( plus a TTL converter to make it serial) so I can just display distance. No need to make it complicated. This is why I used a RaspberryPi zero.
The software is quite important to make this bad boy reliable.
The videos were filmed in slow motion and normal rate, really good teaching point if you get the pupils to film the sonar sensor and they will be able to hear the ultra sound at a lower frequency.
When finished I will box, and try and make resiliant and pretty looking.
The code available here