Planet Arduino

Long range wireless control of a project is always a challenge. [Mike] and his team were looking to extend the range of their current RC setup for a UAV project, and decided on a pair of Arduino mini’s and somewhat expensive Digi Xtend 900Mhz modems to do the trick. With a range of 40 miles, the 1 watt transceivers provide fantastic range. And paired with the all too familiar Arduino, you’ve got yourself an easy long range link.

[Mike] set the transmitter up so it can plug directly into any RC controller training port, decoding the incoming signal and converting it into a serial data package for transmitting. While they don’t provide the range of other RF transmitters we’ve seen, the 40 mile range of the modem’s are more than enough for most projects, including High Altitude Balloon missions.

The code for the Arduino transmitter and receiver sides is available at their github. Though there is no built-in error correction in the code, they have not had any issues.  Unfortunately, a schematic was not provided, but you should be able to get enough information from the images and datasheets to construct a working link.

[Vincent] plays around with remote control tanks, and even though his current model is a WWII-era armor piece, he’d still like modern accoutrements such as a fire control computer and laser sighting for his main gun. His latest project did just that (French, Google translation) with the help of an Arduino, a few modifications to the receiver, and an IR rangefinder.

The stock RC tank includes servos to move the turret and the requisite electronics to fire an Airsoft gun. The precision of the mechanical movements inside the turret weren’t very precise, though, so [Vincent] had to gear down the servos to turn large movements into slight adjustments. After that, he installed an IR rangefinder and laser diode onto the barrel that allowed the gun to sight a target and read its distance.

After some experimentation with the rangefinder and laser, [Vincent] plotted data from firing a few BBs at a whole bunch of distances and targets. The graph came out fairly linear, and after plugging this into a graphing calculator, he was able to find an equation that took into account the distance and angle so the Arduino-powered fire control computer would hit its mark.

The accuracy of the gun is very impressive, all things considered. [Vincent] is able to accurately fire BBs downrange and hit an 8×12 cm target at five meters. You can check out that action below.

[nickatredbox] keeps up to date with the improvements of his project [yellow plane]. As you can find on this blog, the project is evolving week by week. Let’s see what’s today submission

1200 mm Wing space
280 mm cord
14% Clark Y
Target AUW 1300 Grams

Missing battery and camera box have a design which should weigh 140 grams empty.
The assembly shown below weighs 684 Grams no motor or electronics.
Electronics shown weigh 110 grams ESC Arduino board, Xbee, antenna and Gyro board
Motor & prop another 120 Gram

Here you have a [video]  and there you can follow the project on the [website]

We hope [Kabir's] driving skills are top-notch because the camera stuck to the front of this toy is a high-ticket item. It’s ironic, since the donor toy for this hacked RC car only cost about five bucks. It had been gathering dust in the dark reaches of his bedroom until he sat down and gave it a proper upgrade.

He started the project by getting rid of the stock battery and moving to a pair of Lithium Polymer cells. They give the vehicle more power and more than twice the running time between charges. A couple of springs were added to the suspension system for a smoother ride. Turning had been a problem since the original design offered no control over how far the wheels turn. You can just make out the body of the servo motor he rolled into the system to allow for more precise turning.

The most recent addition is the HackHD camera on the front of the vehicle. It records to an SD card rather than streaming the video in real-time. Check out the clip after the break to see the interesting perspective achieved by filming so low to the ground. The one thing we would add is a cage around that board which retails at around $165.

[nickatredbox] has sent this interesting project with Arduino involving wireless comunication. The fun comes when you have to decide to buy something already done or DIY.

I wanted a remote control system of my own design for may various RC model projects planes and boats. I set about researching the options and and Xbee with / Arduino solution poped out as a viable option, having failed performance testing using both WiFi and TinyCLR. The other feature I get as the Xbee is a transceiver is real-time telemetery. I’m sure I could buy this functionality from HobbyKing but where is the fun in that.

More project on the [website]

Hello readers

Today we continue down the path of analog electronics theory by stopping by for an introductory look at the RC circuit. That’s R for resistor, and C for capacitor. As we know from previous articles, resistors can resist or limit the flow of current in a circuit, and a capacitor stores electric current for use in the future. And – when used together – these two simple components can be used for many interesting applications such as timing and creating oscillators of various frequencies.

How is this so? Please consider the following simple circuit:

When the switch is in position A, current flows through R1 and into the capacitor C1 until it is fully charged. During this charging process, the voltage across the capacitor will change, starting from zero until fully charged, at which point the voltage will be the same as if the capacitor had been replaced by a break in the circuit – in this case 6V. Fair enough. But how long will the capacitor take to reach this state? Well the time taken is a function of several things – including the value of the resistor (R1) as it limits the flow of current; and the size of the capacitor – which determines how much charge can be stored.

If we know these two values, we can calculate the time constant of the circuit. The time constant is denoted by the character zeta (lower-case Greek Z).

The time constant is the time taken (in seconds) by the capacitor C that is fed from a resistor R to charge to a certain level. The capacitor will charge to 63% of the final voltage in one time constant, 85% in two time constants, and 100% in five time constants. If you graphed the % charge against time constant, the result is exponential. That is:

Now enough theory – let’s put this RC circuit to practice to see the voltage change across the capacitor as it charges. The resistor R1 will be 20k ohm, the capacitor 1000 uF.

Our time constant will be R x C which will be 20000 ohms x 0.001 farads, which equals 20 (seconds).  Notice the unit conversion – you need to go back to ohms and farads not micro-, pico- or nanofarads. So our example will take 20 seconds to reach 63% of final voltage, and 100 seconds to reach almost full voltage. This is assuming the values of the resistor and capacitor are accurate. The capacitor will have to be taken on face value as I can’t measure it with my equipment, and don’t have the data sheet to know the tolerance. The resistor measured at 19.84 k ohms, and the battery measured 6.27 volts. Therefore our real time constant should be around 19.84 seconds, give or take.

First of all, here is a shot of the little oscilloscope measuring the change in voltage over the capacitor with respect to time. The vertical scale is 1v/division:

And here is the multimeter measuring the voltage next to a stopwatch. (crude yet effective, no?)

The two videos were not the most accurate, as it was difficult to synchronise the stopwatch and start the circuit, but I hope you could see the exponential relationship between time and voltage.

What about discharging? Using the circuit above, if we moved the switch to B after charging the capacitor –  and R2 was also 20k ohm – how long would it take to discharge the capacitor? Exactly the same as charging it! So one time constant to discharge 63% and so on. So you can take the graph from above and invert it as such:

How can we make use of an RC circuit?

I’m glad you asked. Consider the following circuit:

When power is applied, the capacitor starts to charge, and in doing so allows current to flow to the emitter of the transistor, which turns on the LED. However as the capacitor charges, less current passes to the base of the transistor, eventually turning it off. Therefore you can calculate time constants and experiment to create an off timer. However, a preferable way would be to make use of a 555 timer. For example, an RC combination is used to set the pulse length used in astable timing applications, for example using R1, R2 and C1:

(For more information on the 555 timer, please read this article)

Another use of the RC circuit is oscillating. Due to varying capacitor values due to tolerance, you most likely cannot make precision frequency generators, but you can still have some fun and make useful things. Here is a classic oscillator example – an astable multivibrator:

What is going on here? Here it is in action:

and here is one side being measured on the little scope:

We have two RC circuits, each controlling a transistor. When power is applied, there is no way to determine which side will start first, as this depends on the latent charge in the capacitors and the exact values of the resistors and capacitors. So to start let’s assume the left transistor (Q1) and LED are on; and the right transistor (Q2) and LED are off. The voltage at collector of Q1 will be close to zero as it is on. And the voltage at the base of Q2 will also be close to zero as C2 will initially be discharged. But C2 will now start charging via R4 and base of Q1 to around 5.4V (remember the 0.6v loss over the base-emitter junction of a transistor). While this is happening, C1 starts charging through R2. Once the voltage difference reaches 0.6V over the capacitor, Q2 is turned on.

But when Q2 is on, the voltage at the collector drops to zero, and C2 is charged, so it pulls the voltage at the base of Q1 to -5.4v, turning it off and the left LED. C1 starts charging via R1, and C2 starts charging via R3 until it reaches 0.6v. Then Q1 turns on, bringing the base of Q2 down to -5.4V – switching it off. And the whole process repeats itself. Argh. Now you can see why Arduino is so popular.

Time for a laugh – here is the result of too much current through a trimpot:

So there you have it – the RC circuit. Part of the magic of analogue electronics!

As always, thank you for reading and I look forward to your comments and so on. Furthermore, don’t be shy in pointing out errors or places that could use improvement. Please subscribe using one of the methods at the top-right of this web page to receive updates on new posts. Or join our new Google Group.

Otherwise, have fun, be good to each other – and make something!