EXHIBIT 5.1



            [LETTERHEAD OF GRAY, PLANT, MOOTY, MOOTY & BENNETT, P.A.]



April 29, 2003

HEI, Inc.
1495 Steiger Lake Lane
Victoria, Minnesota 55386
RE: Form S-3 Registration Statement

Gentlemen:

     This opinion is furnished in connection with the registration, pursuant to
the Securities Act of 1933, as amended, of 1,000,000 issued and outstanding
shares of common stock of HEI, Inc. (the "Company") to be sold by Colorado
MEDtech, Inc. and Eastside Properties, LLC (the "Shares").

     We have acted as counsel to the Company in connection with the preparation
of the Registration Statement on Form S-3 (the "Registration Statement"). We
have examined the Amended and Restated Articles of Incorporation, the Amended
and Restated Bylaws of the Company, such records of the proceedings of the
Company as we deemed material and such other certificates, records and documents
as we considered necessary for the purpose of this opinion.

     Based on the foregoing, we are of the opinion that the Shares are legally
issued, fully paid and non-assessable securities of the Company. We understand
that this opinion is to be issued in connection with the Registration Statement.
We consent to be named under the caption "Legal Matters" in the Prospectus,
which constitutes a part of the Registration Statement. We further consent to
the filing of a copy of this opinion with the Registration Statement.



                                   Very truly yours,

                                   /s/ Gray, Plant, Mooty, Mooty & Bennett, P.A.