Lotus Elan ALDL Interface Circuit

Getting your hands on an interface

You are one of two types of people:

Type 1: I'm going to make my own. Its a simple circuit, how hard can it be?
Type 2: What are you mad? Do I look like I was dropped on my head? Tell me where to buy one now you muppet!

Type 1s: read on and check out the links below
Type 2s: try these links (you ingrates)

Easy home build solution

My latest interfaces are based on a readily available pre-made circuit from active robots. It can be purchased here. It is powered from the USB port so only the ground and the data line from the ALDL port need to be connected. The Rxd and Txd pins must be connected together and connected to the ALDL data line and the ground from the ALDL must be connected to the ground pin on the circuit.

USB circuit

Drivers for it can be found here

Or if you enjoy soldering

My first circuits were based on Ian Levy's as, at the time,  it was the only circuit I knew had worked with an Elan. His circuit can be found at http://www.syntaxis-technology.co.uk/lotus/hardware.html. In fact any of the 8192 baud ALDL circuits out there should work.

Below are stripboard layouts of a slightly modified (IC1 changed to MAX233/MAX232, output voltage changed from Vbat to 5V and the input threshold level lowered slightly) version of the circuit mentioned above. I've built all these designs and they worked for me. If you copy any you take your chances. If your computer catches fire, your house burns down, your car explodes, your significant other leaves you and your dog moves next door I'm sorry but that's it.

MAX233CPP circuit version 1Max233 circuit V1
Ok just a bit bigger than it needs to be.

MAX233CPP circuit version 2Max233 circuit V2    Max233 circuit V2
Slight changes in comparator voltage thresholds, made more compact, space opened to allow regulator to be leaned over a little more.

MAX232CPE circuit version 1Max232 circuit V1    Max233 circuit V2
Cheapest of the three in terms of components, compact - recommended (nb prototype pictured - extra capacitor included).

The 'x's on the diagrams indicate where tracks should be cut. All the tracks between the legs of the ICs should also be cut.

For the 7805 regulator pin 1 (input) goes on the 12V rail (track 2), pin 3 - the middle pin for some reason - (gnd) on the ground rail (track 3), and pin 2 (output) on the 5V rail (track 4). I think its the same for the LM2931A - check. So, as you look at the figures above, the heatsink of the regulator should be on the right.
All the  bits are available from RS components.

I inked in the track numbers and the component positions on the board before I started soldering. Use a small tip on the iron and don't use one thats too powerful - its easy to fry the Si bits (use sockets for the ICs). If you aren't confident at soldering practice on a spare bit until you can put joints on the board quickly and reliably without crossing tracks. It doesn't have to be pretty. Once you've finished check it thoroughly visually and if you can with a meter for errors and joined tracks.

Once you've made it the acid test is to power it and connect it to the PC. Start hyperterminal set it to the COM port you're connected to and type in some characters if they echo it works! If not unplug and check it again.

       Links to DIY ALDL interface stuff

Tech Edge - No power lead required!
Andy Whittaker - Good selection of circuits. (The two transistor circuit works!)

Want to buy one instead?

          makinterface (Germany) - If you have one and it works with ElanScan let me know.
AKM cables (US) - If you have one and it works with ElanScan let me know.
Andy Whittaker (UK) - Known to work. Provides ALDL connectors as well.
TTS Power Systems (US) - If you have one and it works with ElanScan let me know.
Wide Open throttle Electronics (US) Known to work but not with 100% of PCs