If you run within 150 air miles all the time, you would not require an eld. If you exceed 150 air miles fewer than 8 times in a rolling 30 day period, you would also be exempt. More than 8 times in 30 days rolling, then you would need eld.
@Bean Jr. hit the nail on the head. It doesn't matter if you pass an occasional weigh station. What matters is how far you drive, how many hours you are out, and if you go back to the same place you started at the end of the day.
Since we are being picky... It matters if the load crosses a state line, not so much the driver.
The actual vehicle does require an ELD. Now like mentioned there are exceptions.
There currently is no state that requires an ELD for intrastate loads. There is the 150 mile timecard exemption. One of the few times on duty time is regulated as it has a 14 hour on duty/driving requirement.
There is also agriculture exemptions in most states. Even package delivery has it's own HOS sometimes.