The SECO Model 250 Transistor and Tunnel Diode Tester

This is a quite rare device I picked up on Ebay some years ago, for testing transistors and diodes, including tunnel diodes.

 

The instructions are on a label pasted to the inside of the cover, and are unfortunately in a sorry state.

Here’s a better image from a recent (2012) Ebay auction for the same type of tester:

Instructions (found elsewhere)

Arduino based hexapod robot

This is a project I’m working on: a six-footed robot controlled by an Arduino processor.

The Arduino is a Duemilanove with a BMA180 accelerometer shield attached (this is used for dead-reckoning of the robot’s movement). There are six “legs” using twelve servos (HobbyKing HK15138 rated at 3.8kg @ 5V) arranged radially in pairs around a central platform. The upper servo on each leg is mounted horizontally and controls the leg twist. The lower servo is mounted vertically and has a short dowel foot that can rotate in the vertical plane.

The servos are powered from a separate 5Volt high current supply (from an old Sun desktop workstation) that can deliver several amps. The servos are attached to a servo board made from a small piece of Veroboard which shares a common ground with the Arduino.

The Arduino code uses the servos.h library to position the servos. Here is the code:


// Control code for the hexapod
// JJB 2012

#include

Servo legServo[6];
Servo footServo[6];
// angles for each foot servo so that the foot is vertical
int zeroFoot[6] = {60,90,100,95,95,95};
// angles for each leg servo so the servo arm is at right angles to the platform
int zeroLeg[6] = {120,100,95,90,110,100};
int maxangle = 45;
int NLEGS = 6;

void setup() {
Serial.begin(9600);
Serial.println("Attaching servos:");
for(int i=0;i<NLEGS;i++) {
int ileg = 2*i+2;
int ifoot = ileg+1;
legServo[i].attach(ileg);
footServo[i].attach(ifoot);
Serial.print("Leg ");
Serial.print(i);
Serial.print(" Leg servo pin ");
Serial.print(ileg);
Serial.print(" Foot servo pin ");
Serial.println(ifoot);
}
centreServos();
}

void centreServos() {
Serial.println("Centre servos");
for(int i=0;i<NLEGS;i++) {
legServo[i].write(zeroLeg[i]);
//delay(2000);
footServo[i].write(zeroFoot[i]);
//delay(2000);
}
}

void crouch() {
Serial.println("Crouch");
for(int i=0;i<NLEGS;i++) {
footServo[i].write(zeroFoot[i]-maxangle);
}
}

void stand() {
Serial.println("Stand");
for(int i=0;i<NLEGS;i++) {
footServo[i].write(zeroFoot[i]);
}
}

void liftFoot(int i) {
footServo[i].write(zeroFoot[i]-maxangle);
}

void rotateLeft() {
Serial.println("Rotate Left");
for(int i=0;i<NLEGS;i++) {
legServo[i].write(zeroLeg[i]-maxangle);
}
}

void rotateRight() {
Serial.println("Rotate Right");
for(int i=0;i<NLEGS;i++) {
legServo[i].write(zeroLeg[i]+maxangle);
}
}

void liftFootSet0(int dir) {
// dir = +1 forward, -1 backward
footServo[0].write(zeroFoot[0]-(dir*maxangle));
footServo[2].write(zeroFoot[2]+(dir*maxangle));
footServo[4].write(zeroFoot[4]-(dir*maxangle));
}
void liftFootSet1(int dir) {
// dir = +1 forward, -1 backward
footServo[1].write(zeroFoot[1]+(dir*maxangle));
footServo[3].write(zeroFoot[3]+(dir*maxangle));
footServo[5].write(zeroFoot[5]-(dir*maxangle));
}

void lowerFootSet(int i) {
footServo[i].write(zeroFoot[i]);
footServo[i+2].write(zeroFoot[i+2]);
footServo[i+4].write(zeroFoot[i+4]);
}

void swingLegSet(int i) {
legServo[i].write(zeroLeg[i]-maxangle);
legServo[i+2].write(zeroLeg[i+2]-maxangle);
legServo[i+4].write(zeroLeg[i+4]-maxangle);
}

void rotateLeg(int i, int dir) {
legServo[i].write(zeroLeg[i]+(dir*maxangle));
}

void tripodWalk(int nsteps) {
centreServos();
// align first tripod feet
legServo[0].write(zeroLeg[0]-maxangle);
legServo[2].write(zeroLeg[2]);
legServo[4].write(zeroLeg[4]+maxangle);
// align second tripod feet
legServo[1].write(zeroLeg[1]+maxangle);
legServo[3].write(zeroLeg[3]-maxangle);
legServo[5].write(zeroLeg[5]);
delay(1000);

for(int i=0;i 0) {
int inbyte = Serial.read();
switch (inbyte) {
case 't':
tripodWalk(10);
break;
case 'c': // crouch
crouch();
break;
case 'i': // init - centreServos
centreServos();
break;
case 's': // stand
stand();
break;
case 'r': // rotate left
rotateLeft();
break;
case 'R': // rotate right
rotateRight();
break;
default:
break;
}
}
}

Here is a video of the hexapod walking. It’s not very efficient!

Quadcopter: more progress

Now I have the quadcopter fully wired up and operational. I had various wiring problems with it initially, which were solved by enquiries over at the AeroQuad forums. The first was that I had assumed all the motors should be wired up with the same polarity from the ESC, and that the AeroQuad software would take care of setting the direction (a quad needs two clockwise rotating impellers, say at the front and back, and two counter-clockwise, say at the left and right). This was not the case: the simple solution was to swap two of the three motor wires on the left hand and right hand motors. The front and rear motors rotate clockwise, so they need “pusher” props – I am using 8×6 types. The right and left require standard props – I am using 9×4 types. The other wiring problem I had was due to the fact that I’m using an older AeroQuad shield (v1.7) with newer software (v3.0.1) – the shield labels the motor ESC outputs in order as “Front Right Rear Left” but the software has a different order (it can in fact be changed in the configuration) – so I had to swap the ESC leads between the Right and Rear positions on my shield.

Here is a view of the wired up quad’s central pod, made with a RubberMaid food container that was a perfect fit.

Quad central pod, showing wiring and battery attachment.

Notice the on-off slider switch for supplying power from the battery to the Arduino and the motors. Also notice the battery mounted underneath the quad: this is a 2560mAh Turnigy LiPoly flatpack, attached by velcro strips. A view of the underside:

Showing the method of hanging the battery securely under the quad.

The AeroQuad software comes with a “Configurator” that is used to calibrate the sensors and the transmitter. I used this, and in the process found that one of the channels on my transmitter was operating in the wrong direction for the software. This was cured by using a software tool for configuring the HobbyKing 6ch transmitter, which allowed the swap of direction of any channel.

After calibration and fiddling about, I made several attempts to fly the quad, or at least to lift off vertically. It was not a success as the video shows:

After several crashes I found that the pusher props were loose, and the motor mounts had been bent out of line. So I had to fix those problems before continuing …

Quadcopter Progress

I’ve been putting the quadcopter construction (first described in this post) on hold for quite a while, for a couple of reasons. One was that I needed to come up with an idea for the frame, and the other was that I was unsure if I really wanted to build such a dangerous toy! Basically, the thing has four pairs of knives (the propellers) rotating at high speed, on a device that is potentially uncontrollable while airborne – not a reassuring prospect.

Putting the second reason aside for the moment (the quadcopter is only dangerous once the propellers are fitted, and I’m a long way off that point), I started work on the frame.

First I built four small motor platforms for the TowerPro BM2410-08T brushless motors using short lengths cut from of a strip of poplar. To each I attached a small 1/2″ cable clamp into which I inserted one end of each of the four helicopter booms that I’m using for the struts.

Motor mounts

Struts with motor platforms and motors attached.

For the central platform (which will hold the Arduino, RF receiver and battery pack), I cut a 5 1/2″ square of poplar board, drilled a central hole, then attached the four struts using more cable clamps and a central bolt and large washer that presses down on each of four rubber grommets that I placed at the end of each strut.

Method of attaching the four struts/booms to the central platform

After tightening all nuts, the whole frame feels quite solid and stable. It remains to be seen how it will stand up to the high level of vibrations expected!

View of the topside of the completed frame.

Repairing a Sharp Optonica RP-117H

This turntable was bought on Ebay “for repair”. The first problem was that the turntable tray was loose and wouldn’t retract or come out. On removing the covers, a shield over the tray motor and the motor itself it was obvious what the problem was:

Broken tray gear wheel

The gear wheel is split, and has dropped off the motor drive. Here is a close-up of the gear:

Closeup of gear

Because the gear had shrunk a little (probably why it cracked), simply epoxying it together at the crack didn’t work: this made the hole too small and prevented the gear from going back on to the drive shaft. I carefully bored the hole out a tiny amount, then used epoxy to glue the crack and the gear back onto the shaft: I clamped it there for 24 hours.

Next problem was a broken belt for the platter itself: to reveal this involves removing a plate underneath the turntable tray:

Broken belt on motor

The belt had disintegrated, leaving a rubbery mess over the turntable and the motor capstan – removed fairly easily with rubbing alcohol. I ordered a replacement belt, and fitted it by feeding it through from the top of the turntable. It was a bit fiddly, but I’d read somewhere it was a nightmare – I didn’t find that.

Now the turntable tray moved in and out, and the turntable turned. The next problem was that the stylus trays were not moving. These trays move linearly across the deck. There is a clever mechanism with worm gears and a slotted metal disk and opto-transistors that move and detect where each stylus arm is. Here is the mechanism:

Stylus trays mechanism

Just visible at the back of the mechanism is a rubber belt – of course this turned out to be worn and was slipping on the motor and not moving the mechanism. I replaced it with a rubber belt I happened to have in my parts box and fit very nicely. Now the whole mechanism worked. Here is a video of it in operation, showing the switchover to Side B from Side A, which involves the turntable motor reversing direction.

The fitted stylii are by AudioTechnica. The Sharp part number is STY133.

AudioTechnica Stylus

Although the turntable now works, it initially played several LPs without issue, it has now developed a random periodic click/thump, almost as if the record is scratched. This is a little peculiar and hard to understand. To be continued ….

Sharp Optonica RP-117H and Sony CDP-X555ES

Bought a beachfront condo/cottage in Hawaii!

We have bought the cottage unit we’ve been going to on holiday to for the past few years. It came up for sale, and seems like the ideal combination of investment and holiday place. Plus we can rent it out when we’re not there. The whole process of buying it took about 100 days from start to finish, due to an insane amount of repeated paperwork and various delays, but finally the escrow closed today

Anyway, here it is!

Replacing a Celestron PowerSeeker 127EQ Tripod with Something More Sturdy

We have a 4 1/2″ reflector telescope (an Orion StarQuest) which is on a Dobson mount. I got fed up constantly having to reposition the scope while watching e.g. Jupiter, as what I was watching moved out of view. I decided I needed an equatorial mount with a motor drive, and started looking around to see if I could find a mount that would fit the StarQuest scope, but the mounts I found were all very expensive. In the end, I bought a Celestron 127EQ (see Figure 2) which came complete with a German Equatorial mount, for the princely sum of $116 on Amazon.I also ordered a Celestron AstroMaster motor drive (Figure 1), and a Celestron 93625 T adapter and a Fotodex T adapter mounting ring that would allow me to attach my Canon Digital Rebel XSi to either scope (they both have 1.25″ eyepiece tubes).

Figure 1: Celestron motor drive

After assembling the Celestron and fiddling about playing around and understanding the EQ mount, I realised that the supplied tripod was going to drive me nuts: it wobbled and swayed even if I breathed on it. I tried tightening everything up as much as I could, but it still wobbled – it was far too flimsy.

Figure 2: Celestron PowerSeeker 127EQ Newtonian Reflector

So I decided to make something a little more sturdy using bits and pieces I had in the garage. Here are the parts I collected:

• 1 Circular piece of 3/4″ thick plywood, diameter 24″ – base board
• 1 Circular piece of 3?4″ thick plywood, diameter 12″ – scope platform
• 1 5ft length of 4″x4″ wood stock – pillar
• 4 shelving brackets
• 4 3″ steel brackets
• 3 screw thread furniture feet
• 3 nuts to fit the feet
• 4 3″ lengths of 2 1/2″x3/4″ wood stock

Step 1:

Find the centre of the 24″ diameter circular base board: drill a pilot hole through the board there. Place the end of the 4″x4″ pillar upright at the centre of the base board, position the four shelving brackets against the sides of the pillar, mark screw hole positions in the base, and then screw the brackets in place on the base board.

Step 2:

Remove the pillar from the base board, turn the board upside down, then place the base board on the top of the 4″x4″. Drive a long screw through the board, into the 4″x4″, then drill a couple more holes nearby, and drive long screws into those, too.

Step 3:

Turn the board and pillar right way up, carefully supporting the pillar. Now attach the brackets to the pillar with screws, and tighten all screws very tight.

Step 4:

Take the four 3″ steel brackets and attach each to each of the 3″ lengths of wood stock with screws. Then loosely attach each combination to each side of the top of the pillar so that they are centred and level. These will act as spacers so that one can gain access to the nut at the centre of the EQ mount to tighten it.

Step 5:

Using a jigsaw, cut a circular hole in the centre of the scope platform board, of the same diameter as the circular part of the Celestron tripod platform (see Figure 3).

Figure 3: Celestron tripod platform, with new holes drilled at the top of each spoke

Step 6:

Remove the legs from the Celestron tripod, leaving the platform for the EQ mount, and put the threaded rods and nuts that secured the legs to one side. See Figure 3. Drill a hole through the top of each “spoke” of the platform: these will be used to pass the rods through and tighten the platform to the board.

Figure 4: The scope platform showing the spacers and brackets attached to the pillar

Step 7:

Place the scope platform board on top of the spacer/brackets, mark and drill pilot holes through the board into the spacers, and screw tightly in place. Then firmly tighten the brackets against the top of the pillar. See Figure 4.

Place the tripod mount on top of the platform, centre it, and carefully mark the positions of the three spoke holes, using an awl. Before drilling through, make sure that the positions are clear on the underside of the board, and wont foul any of the platform supports.

Step 8:

The platform board should be fairly horizontal at this point, but it’s not critical as there will be adjustable feet added to the base board. These will require captive nuts. Turn the whole mount upside down so that it is resting on the scope platform. Using the centre of the base board, and a protractor mark positions for the three feet at 120 degrees from each other, about 2″ in from the edge of the board. Find three nuts that will fit on the screw feet. Using e.g. a Forstner bit, drill large diameter holes just bigger than the diameter of the nuts, part way through the base board. Find a drill just smaller in diameter than the screw thread on the feet, and drill through the centre of the holes to the other side of the board. Test to make sure that the feet than be screwed in and out of the holes. See Figure 6.

Step 9:

Using a two part epoxy, glue the captive nuts into the holes, taking care that the nuts are centred and that no glue gets into the threads. Leave the epoxy to set. See Figure 5.

Figure 5: Captive nut and adjustable foot

Step 10:

Sand all surfaces, clean with a rag, and then spray paint your choice of colour. (I had a bunch of Rustoleum Navy Blue indoor/outdoor aerosols left over from another project, so I used those.) Leave to dry well.

Figure 6: Mounting the captive nuts and adjustable feet to the base board

Step 11:

Mount the Celestron tripod platform to the scope platform board, using the threaded rods and nuts that came from the tripod. Screw in the three adjustable feet at the bottom of the base board. The platform is now ready to use.

Figure 7: Painting the mount

Here is the finished mount (Figure 8) with the PowerSeeker 127EQ attached. There is a minor problem: the counterbalance for the scope touches against the scope board for low inclinations to the horizon. This will simply require the scope board to be reduced in diameter by taking a circular cut around it – but I haven’t bothered since the viewing area is surrounded by high walls anyway.

Figure 8: The completed home made mount, with Celestron PowerSeeker 127EQ