I would love one of these to go with my pitch trim.
A friend that builds a lot of electrical things says it's as easy to build several as it is to just do one, and the price of the boards goes down with quantity. The fellow that designed it quit making them.
From his web site:
Altitude Hold Unit
Description & Specifications
What is it?
The Ez-Trim is a small low cost unit that provides basic altitude hold function for homebuilts. I wanted a economical unit for my E-Racer canard. I could not find one, so I started designing my own. After several months and over half a dozen different test units, I had a unit that worked. It has been used and tested with a MAC pitch trim servo attached to the PTH trim lever and the Strong pitch trim servo. It will maintain the selected altitude very well in smooth air conditons. In turbulence it will keep trying but you may prefer to fly manually. The key is getting the unit adjusted to the plane properly using the response adjustments provided. It has front panel adjustment screws to allow you to adjust its response to your particular homebuilt.
It is intended to provide missing altitude hold when used with a wing leveler like the Navaid Devices unit. It sends control to the relays that control the electric pitch trim servo. The unit is designed to provide altitude hold function using a pitch trim servo through relays. The unit does not have the current capacity to directly drive the servo.
Since the unit controls using the pitch trim it is easy to override if there is a malfunction.