NEW MOSFET SWITCHING BOARD BUILT AND WIRED IN
I had verified using LTspice that the circuit behaves correctly and achieves everything I want. In this approach, the MOSFETs pass the voltage through to the 1130 circuit almost identically to how a mechanical switch would.
It did add a transistor to each of the four switched signals, in order to switch the gate of the MOSFET to a voltage lower than the source. Resistor voltage divider on the gate circuit lets me dial in the voltage differential, to ensure that the MOSFET fully switches on the channel from source to drain.
The new switches were built with P channel MOSFETS driven by an NPN transistor, plus a number of resistors. A quick check on the breadboard verified the behavior with the exact components, then I soldered this together on a perf board just like the previous one. After replacing the prior switch board inside the emulator, I was ready to test again.
Due to the high voltage on the switch for the -TWR CB RESPONSE signal, +48V, I had to use a high voltage NPN transistor, BD139, as the usual NPN transistors typically break down with more than 40V across emitter and collector. I had to wait for the part to arrive before I had the entire board completed and wired in place. I was mildly concerned that the transistors were from China, as there is the risk that this is a lower voltage cheaper transistor relabeled as a BD139. This is based on the high rate of chip fraud coming from Asia particularly through outlets like Amazon.
HOPE TO CONVERT ONE OF THE CABLES TO A FEMALE SMS SOCKET
If the 3D printed part arrives in the next couple of days, I will convert one of the two signal cables from a male SMS paddle card to the socket I designed. This will match the polarity of the cables coming from the 1052 typewriter into the 1130. I won't need to wait to begin testing on the system, as I do have a gender changer/adapter temporarily installed.
No comments:
Post a Comment