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Rev2 - Unruly design for lower cost

A project log for Open Source LiDAR - Unruly

We've been waiting a long time for someone to post the plans of a working LiDAR. Is it really going to happen?

Laser DeveloperLaser Developer 02/02/2019 at 14:530 Comments

DESIGN CHANGES

Once the design of a product is complete the hard work begins. The principle of operation and basic functionality remain the same but new constraints must be considered such as the availability and price of parts, ease of manufacture, tooling for lower costs and so on. These constraints make the difference between an idea and a product that can be made and sold. Hence the Unruly Rev2 has:

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TESTS

The boards have arrived and test results are as follows:

1. The first test is to evaluate the performance of a new LiDAR specific TIA from Analog/Linear called LTC6560.

Positives: In terms of sensitivity, noise characteristics, overdrive recovery and stability this is a great component. It provides enough gain that there is no need for a post amplification stage thereby saving on component costs. It operates right at the theoretical limits of performance, meaning that you are not likely to be able to design a better TIA circuit yourself.

Negatives: This device may have limited application in battery powered LiDARs because it needs a +5V power supply. It is also draws more power than the Maxim equivalents. To get full speed operation it needs a pull down resistor on the output which draws additional power.

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CONCLUSIONS

On balance, I have decided not to use the LTC6560 TIA. I think that the requirement of running on a 5V supply will make battery powered operation painful. Everything else runs perfectly on a 3.6V battery so it doesn't make sense to lose that capability.

On the matter of production, LightWare has offered to produce the Unruly provided that we can get the retail price below US$100. Using the MAX4658 TIA is the cheapest option so this fits well with this requirement.

Additionally, we can remove the VGA post amplifier to reduce the price further. This will bring the useful measuring range down to about 60m but for most robotics applications this is more than enough. The maximum range is still beyond 100m but it needs a large white wall as a target.

So, on to Unruly Rev3!

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