These circuits are really simple. Unless the NSA has backdoored solid-state physics it's no greater a risk than this approach. (The NSA very well could backdoor the camera you point at these pendulums).
Hmm, I had to check this and came across this thread on Reddit. NIST has a standard for it, but the exact point is that _that_ can be influenced by them.
Also, somewhere in the thread, they mention that it is probably too hard to verify how it is actually implemented in the hardware.