Simulating 300bps Via Telnet

FozzTexx who runs the /r/retrobattlestations subreddit and Level 29 BBS was looking for a way to throttle telnet sessions to his BBS. He wanted to simulate the connection at 300bps.

As part of my ViewData BBS system I added in the facility to throttle the speed of the connection to give an accurate feel to way that it used to look.

Another item that is implemented is a way to pass through to an external BBS thus allowing me to either throttle or dial into telnet only ViewData BBSs.

My system was designed to handle ViewData only so I did a few adjustments and created a proxy service that will allow the connection to another BBS but will throttle the speed.

Connecting...

To connect to the Level 29 BBS with throttling enabled you can telnet (RAW) to the following ports...

Connect to - bbs.retroacorn.net

Port 6000 - 300bps
Port 7000 - 1200bps
Port 8000 - 2400bps

When I get the time I might add in a menu system to allow connection to other BBS systems.

Fixing In Place

Started by cutting down the main power board using the dremel and hot gluing it in place.

Wiring It Up

Wired up the harness to connect the VGA convertor board to the TTL RGB output of the BBC. The hooks will be connected to the resistors on the inside of the board. This means that I don't have to solder the entire lot to the board.

Just need to trim down the board using the Dremel.

Sorted out the power switch which will allow me to switch between the external power and battery.

Next job is to wire up the internal power to all of the above items.

Cutting Tracks

Had to do the bit I was not looking forward to. Cutting through the power tracks on both sides of the board.

Was a bit worried about damaging the board but was careful to remove the track with a Stanley knife without damaging anything else.

Gluing Bits In Place

Glued the power connections in place to stop then moving and protect the board.

Added in fixings for VGA convertor board.

VGA convertor board now fixed on mountings.

Soldering Power To The Main Board

After about an hour of fiddling around managed to solder the 4 wires which will take the power from the external socket to my board and back. The solder on the machine is lead and it does not want to melt. I had an absolute nightmare getting the wires through the board and getting the solder to melt on both sides. Finally after lots of fiddling got the wires soldered on.

Next tested that it actually will work from the battery. Machine initially kept powering off after a few seconds. I found the reason, i'd managed to short two of the connections on the back my perf board. Sorted that out and it works ok.

Next thing to do is cut the tracks so that the input wires are separated from the output ones, the input will power the charger and the VGA convertor board. The power from the battery board will then go back into the machine (or be powered via the input if the switch is in the correct position).

VGA Convertor

Due to the VGA converter drawing lots of power I have decided to make it available when the machine is powered via mains. It adds too much drain to the battery and is not really useful unless you are at a desk anyway.

Originally I was going to have everything powered by the battery and the unit could be powered off via a switch but would always be charging if plugged in.

The machine will now do the following...

1) Always charge when plugged in.
2) The VGA convertor will be powered when plugged in only (from the incoming 5v).
3) The machine can be powered externally while the batteries are charged or you can use the battery to power the machine and the small screen. Thus the small screen is only available when on battery power and turned on. Where the machine is available if using battery or on external power (as the original machine was) dependant on the switch position.

Battery Testing

Tested the battery (2000mah) and found that with the small screen and the machine powered it will provided about 45mins to an hour. Have managed to get the battery I was originally going to order (but was out of stock) which is 6000mah so gives several hours of usage.

Screen

Mounted the screen in the case.

Firstly marked out where the screen should go and used the dremel to cut out the hole. I left a small set of lugs from the lower plastic area so that the screen can sit on them. It turns out the screen was exactly the same height as the indent in the air slots so it fits nicely.

Inserted screen and adjusted to fit correctly.

Hot glued the screen and the board into place.

Tested to check everything works ok.

Installed SD Card

Dismantled the Compact and installed the GoSDC into the ROM slot.

TV Display

Tried to power the small TV display from the machine but found it requires 6v. Going to have to add another Step-Up to the power board to provide the 6v it requires.

Update: Wired in the extra Step-Up, Adjusted the voltages on the Step-Up boards so that one is 5v and the other 6v.

Connected the power board to the BBC externally and checked that everything works ok. Board is powering the screen, Gonbez board and the BBC from the battery.

Then tested the TV board, connected to the external video out and got the following.

You can just about make out the Acorn MOS and the command prompt. This looks better in real life the camera doesn't do it justice. Next step is to get it to run something on the screen.

Battery & Charging Circuit

Well some parts I'd ordered arrived so I decided to solder them together to test out the chargeable battery.

Here is the current charging circuit connected to the mains and the Gonbez. I can remove the power from the main socket and the battery takes over.

This should hopefully provide a 5v input which will charge the LiPo battery when the unit is plugged in. I intend to wire a switch in between the charging board and the step-up board so that I can turn off the machine without stopping it charging.

The charge circuit takes 5v in but the battery is 3.7v. To be able to supply the 5v needed for all the internal boards I am using a step-up board that will take the 3.7v to 5v. I have tried it with the Gonbez board and it runs this ok.

Mini TV Screen

I have a very small TV screen which I bought. The next step is to wire up the screen check it works with the output from the BBC.