Let's Make Robots!


When it's finished it should be able to get me a beer out of the fridge :) or make a mess for me to clean up :(

Updated, improvement to laser range finder. First test with picaxe 14M.


This is the base with the mid section attached. The mid section is driven by a 24V 100W scooter motor and uses an old car bottlejack as a gearbox/drive mechanism. I've added springs at the bottom to counter the weight of the scissor section so the motor doesn't work so hard when it rises. Fully extended, the top is a meter high. This is made from 25x25 and 25x38 aluminium box section.

Unfortunately the gears in the bottlejack are cheap diecast and don't mesh very smoothly. This is fine when turned slowly by hand when jacking up a car but is incredibly noisy when driven at 2500RPM. So that the robot can sense the height of the mid section I'm using a hall effect sensor and a small magnet. This gives me a simple analog 0-5V signal thats easy for the picaxe to read.















This is my cheap laser range finder (about $45). Doesn't work as well as the bought ones and I think it's short sighted as it only has a range of about 600mm at the moment. I wanted a sensor that could more accurately locate a table or chair leg. On the underside of the cpu fan is a small piece of a blank cd glued to the centre of the fan. This spinning mirror directs the laser (5mW red) around the room. The small black tube at the upper right is a phototransistor with a piece of heatshrink on it so it only detects light from in front of it. This signal is amplified by a couple of transistors and mixed with the tacho output from the fan to give me a pulse with a width that represents the angle of the mirror when the phototransistor was hit by the beam. The closer the object, the sharper the angle. The chip at the top is a "D" type flip flop that is used to mix the tacho signal and the pulse from the amplifier. The IC to the right of the laser is a stepper motor driver that is used to rotate the entire assembly and the chip at the bottom is a Picaxe 14M that controls the stepper motor and measures the width of the pulse. This is a slave device. It waits for a request from a master processor, aims in the requested direction, takes several readings that are averaged out and sends the result back to the master.


I've been trying to improve the range of the laser rangefinder.


The oscilloscope is measuring the output of the amplifier. I was using debug in the picaxe basic editor to monitor the distance of my hand but the white sceen in the background was messing with the camera.

As you can see, I'm extreemly jealous of Rik's new setup. The rangefinder with it's new monacle is balanced precariously on the front of the keyboard tray while the keyboard is hanging on for dear life at the back!

The picture that you can't make out is Leela from futurama drawn Tomb Raider style!








Anyway, enough of my jealousy and perverted taste, back to the laser rangefinder!

This was the first time I had the picaxe monitoring the output. Previously I had only tested it with the oscilloscope.

As you can see, I've got a 60mm magnifying glass taped to the front of a cardboard tube and mounted the phototransistor at the focal point. This does work better but I have to work on aligning all the optical components. I need to get the phototransistor / lens in line with the laser. At the moment moving the PCB up and down or tweaking the laser up and down affects the distance it can detect. I did get it to pick up a white object at about 2 meters but with some adjustments to both the optical alignment and the amplifier I think I can increase the range to a useful 3 or 4 meters.

If anyone wants to experiment with their own rangefinder I've attatched a simplified schematic to my blog on the rangefinder plus I'm looking at ways to reduce the size of it. The optical setup I've got here is probably bigger than I need but it was what I had laying about.














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Very impressive - specially the laser thingey caught my interest!

I am approx about 1/10 as smart as you, so I have to make 10 times as simple solutions. I am thinking about this one: http://letsmakerobots.com/node/1833

The reason that I bring this up, is that apparently you have the knowledge on how to detect the reflection of a laser beam. With that knowledge I could take my low-tech version to higher grounds :)

You are saying that you can actually - isolated from all the other smart spinning and flip-flopping - measure the reflection of a laser beam @ 60 centimetres? That is fantastic! Just by using non-amplified LDR's I can only measure bright LED's; my lasers are not strong enough (cool quote, btw)

Would it be possible that you make a REALLY simple drawing for a REALLY non-techie like me on how you hook that up? Just the "sensor".

If I can make a such, I might be able to provide you and everyone with one funky laser range finder.

PS: I mean like REALLY simple. Imagine me as retarded, have no references to anything in the world of electronics, just don't get it, nothing can be implicit ;) Thanks.

I think your smarter than you give yourself credit for. I was blown away by how well your wall racers handled without any proportional steering. That's what made me join up.

 As for Amanda LDR thats exactly how my IR sensors are setup including the fact that they pulse on and off to differentiate between ambiant light and the reflection from an object.  The amplifier I use in the rangefinder is only 2x one transistor amplifiers but they would need to be modified for your design as they are designed for a digital signal. 

Wait until I dig out one of my old text books and I'll post a simple amplifier for analog sensors using a transistor and four resistors.

Doesn't get any easier or cheaper than that.

Oops, sorry Fritz, had just woken up and wasn't with it,  it's the spinning, flipflopping bit that measures the distance. The reason for the laser compared to led's is that you still get a nice bright spot over a big distance.  Your system is great for detecting the presence or absence of an object which is why I have ten IR versions of Amanda LDRaround the base of BoozeBot.

By adding some IR Led's to the white Leds you might detect black objects better. Changing the LDR to a photodiode and adjusting the resistor value to suit should increase the sensitivity and thus distance that you can detect object except it would be the FritzPhototransistor and that's quite a mouthful.

Wow, I am honered :)

But still, I must be stupid, because I cannot even ask a question so it is understandable :D

Let me try to pinpoint:


Here is a laser * Here is a sensor 

When laser shines on object * Sensor detects reflection


No pulsing involved but you use photo-thingeys (that I have not made to work) - and possibly amplifying.

Can you tell me how you set it up so that you (I) can make such a sensor (with photothingeys)?

Sorry if you did answer it / it is in the deleted text or in between.. I did read about old text books - but still, you deleted it, and would that do it?

What a crap post, sorry :D  

Ok, I kinda think I understand almost....

I'll make up a simple schematic/sketch and show you how you could increase your range with photothingey's. Hang about

LDR_vs_PHOTOTRANSISTOR.jpgI've left out the LED's but the diagram on the left should be the something like Amanda LDR.

The phototransistor works the same way.  In my circuit the base of the transistor is unconnected.  Some phototransistors don't even have a base pin.

One advantage of the phototransistor is that the case acts as a lense so that it is more sensitive to light directly in front of it .

F*ck me, it's a diagram, and I understand it :D

Thank you very much for making it.

When I work with resistors, I just try with some different ones, or hook up a lot in one big twist (sometimes a handful, I bought a hge case) till it works. What I am saying is, that I am not sure I have made the 10K, as I would not know. But.. apart from that (most likely important) fact, I have made the setup with the photo-thingeys as you show.. but without anything to measure.

This is good and bad news; Aparently I have done it right, but I could not make it work. I call the setup "a voltage divider", because I think that is what it is. 

Is this all that you use, and can you detect a laser with that? I canoot detect anything with it, but seeing this makes me want to try again.

You are not doing any special tricks apart from this?

Thanks a lot :)

Yep, got it in one. If you look at the schematic for the laser rangefinder in the blog you'll see that the circuit I gave you is the very first part of it minus the amps and crap. you should be able to plug this straight into an analog input of your picaxe28 and read the changes in light.  I could do a simple amp for you but it shouldn't be necessary and might take a bit of experimenting to get it just right.

By mounting Amanda LDR or Amanda Photothingy on a servo you could make a radar setup like

did with his home explorer.

Thanks again. I am starting to be sorry that I did not start a new topic on this, am spamming your robot page, sorry.

However, went down and got some .. LD241 "Phototransistor" .. tha guy told me that

A) That was my photodiode - though it's called a phototransistor
B) There would be PLENTY of datasheets on it on the web; Just enter LD241

- But I am startig to think that this guy and he's parts are my problem. Because it was deja-vu; All the suddne I remembered that it was the same guy selling them to me last time I tried, and last time he said the same about datasheets, and just like last time I cannot find any on the web on it!

When I hook up (and like last time, I bought plenty, so I could start over with fresh parts if I burnt stuff without knowing it) I only get constant values. Depending on which way I turn things, I can (of course) get different values.. but they just stay there - no matter how much flash I try to melt them with, no change in values.. That is; I sometimes get a single digit jump, but I reason that to be other things than the light.

The setup is so simple, even I should be able to make it;


Black Ground, White analouge in, Red 5V+

Any comments, wrong photothingey, or did I make a fool out of myself one way or the other? :)

If no clues, then can you link me a thingey that you know works?

Thanks mate on the other side of the globe :)

Ok, I couldn't find a data sheet (yet) but your problem is that it is a photo diode.  It does need amplification, a phototransistor is a photodiode and a transistor combined with the transistor amplifying the signal.  This is why I used a phototransistor, much easier to use.  If you can't get a refund then I can help you make a suitable amplifier once we find a datasheet.

PS. what is the full number on the part?, in the photo it looks like D2417

Yessir, it was a photodiode, the man in the shop admidded it. I'll leave that out of this thread now.

I got some HFE4000-013 - they have 3 pins; One marked with a pin 1), one connected to the housing 2) , and the last one 3).

But I still cannot make any usefull readings :/

I have tried the setup you where so nice to post, any combinations of legs.

I have tried without the resistor, any combination of legs, specially what I'd think would be the right combination; 1) to V, 2) to G, and 3) to analouge in.

I either get 0, some middle values that are not moving, or some frantic jumping values that do not care about light or dark, just jumping.

I do not know what on earth you can do about it, but at least I have complained somewhere now :)

I hate when that happens!  Nice find OddBot, I wonder if Frits can sell them back to the shop as 1 Giga Ohm resistors !