Don Lancaster's prototype TV Typewriter which is now on display at the Computer History Museum has a surplus keyboard with an ASCII encoder circuit that was published in the February 1974 issue of Radio-Electronics.
dˈɑːn lˈæŋkæstɚz pɹˈoʊɾoʊtˌaɪp tˌiːvˈiː tˈaɪpɹaɪɾɚ wˌɪtʃ ɪz nˈaʊ ˌɔn dɪsplˈeɪ æt ðə kəmpjˈuːɾɚ hˈɪstɚɹi mjuːzˈiəm hɐz ɐ sˈɜːplʌs kˈiːboːɹd wɪð ɐn ˈæski ɛŋkˈoʊdɚ sˈɜːkɪt ðæt wʌz pˈʌblɪʃt ɪnðə fˈɛbɹuːˌɛɹi nˈaɪntiːnhˈʌndɹɪd sˈɛvənti fˈoːɹ ˈɪʃuː ʌv ɹˈeɪdɪˌoʊᵻlɛktɹˈɑːnɪks.