### Rangefinders: Lidar Lite V2, Lightware, and others, need recommendations

After near tree months I recived happy the Lidar Lite V2, but now I have a concern because, apparently is discontinued?

something wrong with this thing?

It's a risk to put on my quad? :(

Answer I recived: Lidar was purchased from Garmin, so It's going to re-appear under Garmin name.

Now is in the market Lightware, developing altimeters for Ardu pilot and helping rangefinders users in this forum ( http://www.lightware.co.za/shop/en/4-drone-altimeters. )

I changed the title because this post discussion content look's usefull for other rangefinders too.

#### Replies

• It's ok a 1/4w resistor to plug by pwm?

• For your interest, here is how to calculate the power requirements for a resistor:

The resistor power dissipation (P), in other words how much power in Watts is being converted into heat, depends on the resistor value (R) and the amount of current (I) going through it:

P = R x I x I …………………. Eq 1

In many cases, you don't know what the current (I) is but you do know the voltage (V) across the resistor.

You can calculate the current by using the resistor formula that defines what a resistor is for a given voltage (V) and current (I):

R = V / I …………………….. Eq 2

Rearranging the variables, the current(I) for a resistor value (R) and voltage (V) is given by:

I = V / R …………………….. Eq 3

Now that we know the current (I) and the resistor value (R) we can substitute equation 3 into equation 1 as follows:

P = R x V/R x V/R

Which simplifies to:

P = V x V / R...................... Eq 4

So equation 4 tells us that the power (P) dissipated in a resistor is proportional to the square of the applied voltage (V x V) and inversely proportional the the resistor value (R).

Qualitatively, you can say that the resistor gets a lot hotter if you put more voltage across it but gets cooler if you increase the resistor value.

For the case of a pull-up resistor on an signal line, the typical working voltage is either 3.3V or 5V and the typical resistor value is around 1k.

For the case where the operating voltage is 3.3V, the power dissipation in the resistor is:

P = 3.3 x 3.3 / 1000 = 0.011W

For the case where the operating voltage is 5V, the power dissipation in the resistor is:

P = 5 x 5 / 1000 = 0.025W

As a rule of thumb, if you don't want a resistor to get hot, make sure that it is running at less than 50% of its rated power, so in both cases above a 1/4W resistor will remain quite cool.

• Many thank's Laser, very instructive.

• Cala,

So I found an example of when you should consider a 1/2 watt over a 1/4 watt.  See http://electronics.stackexchange.com/questions/172855/when-to-use-a...

I believe the PWM power is quite low and a 1/4 watt should be safe to use.  But if you test the resistor and it feel hot to the touch while operating the Lidar you may need to jump up to 1/2 watt resistor.  I honestly do not recall the power demands on the PWM pin nor the Lidar Light, but if you are unsure, just use a 1/2 watt and you should be just fine.

• Thank's Doug, the resistor is between signal and ground, not power so, I understand in your article, 1/4 is ok if not use v ? I have 1/4 but, perhaps, for safe better to buy 1/2

•  Resistors lose there voltage accuracy in resistance when they become overheated from too much current draw.  However I don't thing the PWM signals draw much of any current so I'm sure it hooking a 1/4 watt up would work just fine.

• Many thank's Doug.

• Many thank's mark and Randy, I'm going to find the resistor, install, and share results :D

Great photos mark, I have similar mount possibility.

• This is a new guy in town, being tested by FAA.

Now that Garmain has bought out PulseLite You can bet that the price will shoot up quite a bit,

The Latas by Hawk Precision has lot more features, It is in Prototype for now , and no prices or when it will be on the market.

Google is suppose to design something along these lines, but there is nothing from them on the Web right now.

I wanted to purchase a Lidar-Lite v3 but you can't find one on the market, It is suppose to come out again by Garmain as a V4 . So now I will wait and see when the Latas comes out and it's pricing.

Check this out for more info on Latas.