vgavt1593

Marco Maccaferri's Propeller VT100 Terminal, in a box

Overview

This is a remix of Marco Maccaferri's VGA Serial Terminal for RC2014. It is specifically adapted to be used with Stephen C Cousins' SC131 Z180 pocket computer. It fits into the same Hammond 1593N enclosure, making for a neat and tidy setup when combined with an SC131. Of course, it can also be used with any other retrocomputer or device that expects a VT100-like terminal, connected over "TTL-Serial" raw RS232.

VGA terminal stacked with SC131 computer

Terminal description

Details about the terminal itself are covered by Marco's project (this remix largely just changes the form factor). For detailed information, see his project page.

Serial interfaces

Connection to a computer is provided through an FTDI-style pin header, wired to the same pinout. Specifically, it is wired as a DTE (just like an FTDI dongle), so it can be wired directly to a DCE (like an SC131). A second passthrough port is provided to permit a PC connection to the same computer. This passthrough port is wired as a DCE, so FTDI cables can be connected directly. An AND gate mixes the terminal and passthrough connections together, so both can be used simultaneously. Transmitting from both at the same time will send gibberish; in testing this is relatively rare, and XMODEM at least will retransmit if this happens.

Usage

This terminal lets you use your SC131 (or other retrocomputer) standalone, without dependency on another computer. In addition, a modern computer can be connected to the passthrough port as needed. This is useful for sending files over XMODEM, for example.

Power

5V power is received through a standard 5.5/2.1mm barrel jack connection, center positive. The device optionally sends power to the connected computer (selectable by a jumper on JP1 - this is expected by SC131). In most cases, JP1 should be left installed. Wall adapters in this voltage and configuration are common, or a USB to 5.5mm cable can be used (examples here).

Why are the plugs on the front?

Because I ran out of room on the enclosure's panels. Between two FTDI headers, 5V in, reset, power switch, VGA, and USB, there wasn't even room left for a power LED. The serial ports are on the same side as the SC131 ones at least, so those can be connected together cleanly with a 6-pin Dupont cable.

Initial setup

The parts specified are not pre-programmed; they will need to be programmed before use. Either a Prop-Plug can be used on the assembled board, or a TL866 or CH341 can be used on the bare EEPROM. Instructions (and firmware) for programming can be found at the same link as above.

Part selection

Bill Of Materials and part references are below. Note that the right-angle headers have to be a specific type to align with the panel PCBs - they need to have the plastic "end stopper" on the "business" side of the angle, not the side you solder to the PCB. Headers from Pololu, Sparkfun, and Adafruit are like this, as is the Mouser listing below. Most eBay etc listings are not like this, and will not align correctly. If the appropriate headers cannot be sourced, double-row right-angle headers can be used, with the top row of pins removed.

The other headers can be snapped from regular breakaway header, for which eBay is substantially cheaper; the Mouser listings are provided for convenience. The specified parts are just the ones I used, and can be substituted as needed - Mouser links provided for convenience and reference. The case is available in other colours!

Reference	Value	Qty	Mouser link
BZ1	Piezo buzzer	1	TDK PS1240P02BT
C1, C2	1μF ceramic	2	TDK FG18X5R1H105KRT06
C3-C7	100nF ceramic	5	KEMET C315C104M5U5TA
C8	10μF electrolytic	1	Nichicon UMA1E100MDD
J1	5.5/2.1mm barrel socket	1	CUI PJ-002A
J2	1x4 header	1	Amphenol 10129378-904002BLF
J3, J4	1x6 right-angle header	2	Amphenol 10129379-906003BLF
J5	USB A socket	1	Amphenol FCI 87520-1110BLF
J6	D-Sub HD-15 Female	1	TE 2311763-1
JP1	1x2 header	1	Amphenol 10129378-902002BLF
	jumper	1	Harwin M7583-46
R1, R4	10kΩ resistor	2	Yageo CFR-25JT-52-10K
R2, R3	4k7Ω resistor	2	Yageo CFR-25JT-52-4K7
R5, R8	47kΩ resistor	2	Yageo CFR-25JT-52-47K
R6, R7	47Ω resistor	2	Yageo CFR-25JT-52-47R
R9, R12, R15	261Ω resistor	3	Yageo MFR-25FRF52-261R
R10, R13, R16	510Ω resistor	3	Yageo MFR-25FTE52-510R
R11, R14, R17-R19	120Ω resistor	5	Yageo MFR-25FTF52-120R
SW1	SPDT toggle sw, right-angle	1	Grayhill 34CMSP12B2M7QT
SW2	Right-angle tact sw 8.3mm	1	C&K PTS645VL832LFS
U1	Parallax Propeller	1	Parallax Propeller P8X32A-D40
	socket	1	Amphenol DILB40P-223TLF
U2	24LC256 EEPROM	1	Microchip 24LC256
	socket	1	Amphenol DILB8P-223TLF
U3	MCP1700-330	1	Microchip MCP1700-3302E/TO
U4	74HC08	1	TI SN74HC08AN
X1	5MHz HC-49 crystal	1	ECS ECS-50-18-4XEN
Case	Hammond 1593N	1	Hammond 1593NTBU
Screws	Hammond self-tapping	(some of)	Hammond 1593ATS