Problems with Propeller education Kit

Tom Wyckoff

I wired up the breadboards as shown in the instructions. Before inserting any chips I was reading 4.6 volts on the rails. I know this is not good. I tested the LM2937 regulator out of the circuit and found the same voltage. I replaced the LM2937 and got 3.3 volts on the rails. After inserting the chips all was well. Pressing F7 found the chip, and I was able to load the first test pogram and save it to the EEPROM. To check out the EEPROM I disconnected the battery and the Propeller clip, put the battery back on and all was well for a few minutes, then the LED suddenly stopped flashing. After that I was unable to do anything else. Pressing F7 now tells me "no propeller chip was found". Using an oscillosope on Pin 40 of the propeller chip I see what appears to be the probe from the propeller clip, but I never see anything on the reset line or the output of the propeller chip.
First there's a bad voltage regulator, then either the propeller chip or the propeller clip simply failed while running. I also tried a different crystal, I don't have any 5 mhz crystals but I tried an 8 mhz, hoping to see some sort of response, but nothing happened. I am NOT happy! Other than tossing the whole thing in the trash and writing $80 off to experience, do you have any other ideas?

Tom Wyckoff

PatM

Better to email Parallax directly or phone them. They're real good about replacing defective parts. Never had one myself but have seen a few people over the years have duds (nowhere near like XBox failures!) and they all seem to have been made happy.

Paul Baker

Hi Tom, Andy the creator of the Propeller Education Kit likes to diagnose any issues customers have with thier PE Kit. This week he is in New Hampshire teaching educators, so he may be a little delayed in getting to your problem. I will make sure he is aware of your problem and if he has enough time after a day's lecture he will assist you. One thing I can promise you is that we will take care of your problem even if it means replacing your PE Kit.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

stamped

Tom, I can attest to the great support from Parallax (from experience). They will definately get you up and running.

With regards to the Propeller. I have a 40 pin DIP and received two voltage regulators with it. One to drop the input voltage to 5 volts, and another to drop it to 3.3. I found that If I used both the voltage regulators, I ended up with 2.7 volts and the Prop would not run. I removed the 5volt regulator and just ran the 3.3 volt, and when all hooked up I have a steady 3.3 volts on the rails and the Prop runs great. I am unsure why the 5volt regulator was needed? I am certainly no expert on this, so best to get help from the Parallax guys, but just my 2cents.

Tom Wyckoff

Hmmm, I think the dual regulators are there in case you need 5 volts for something. I had 3.3 V on the rails BEFORE installing the chips, and I just checked, it's still 3.28. That should be enough. The weird thing is it was working fine and just stopped. I tested the crystal on another board, it's fine, but my scope doesn't see any oscillations on it either when it's in the propeller kit. Good tip on the voltage regulators, I'll remember that. It might get to be a factor if I start adding stuff to the board.

Fred Hawkins

I've had no problems with the double regulated power supply. That is, until my 9 volt battery got tired. Then everything stopped. A new battery got it going again.

The 5v is used in some of the later lessons, I think.

Just using the single regulator would probably chew up your battery as surplus heat.

Post a picture, maybe we can spot something. Like taking your b+ from the power on led circuit.

RichardF

Tom,
There are two good reasons for using both a 5 volt and a 3.3 volt regulator. To sum up what was previously stated, going from 9 volts to 3.3v directly with these type regulators is going to generate a lot of heat and give poor regulation, and, you will need 5 volts for many TTL applications. Many LCD displays must have a good 5 volt supply. Many sensors must use 5 volts, etc. I suspect this is why Parallax uses them in the PE kit. Personally, I use a 5 cell NiCad pack and don't use the 5 volt regulator. They are cheap and can be recharged.
Regards,
Richard

stamped

Richard it is interesting that you state that going from 9v to 3.3v will generate a lot of heat, as I am doing this and it creates no heat at all. The voltage regulator is not even warm (it has been running constantly for 5 hours). Running through the double regulators had the rails at ~2.7v which would not run the Prop. Removing the 5v had it running at a smooth 3.3v on the rails. I am running 4x1.2v 2500mAh NiMh batteries.

I am no engineer, so my wiring may be incorrect in some way.

Bergamot

stamped said...
Richard it is interesting that you state that going from 9v to 3.3v will generate a lot of heat, as I am doing this and it creates no heat at all. The voltage regulator is not even warm (it has been running constantly for 5 hours). Running through the double regulators had the rails at ~2.7v which would not run the Prop. Removing the 5v had it running at a smooth 3.3v on the rails. I am running 4x1.2v 2500mAh NiMh batteries.

I am no engineer, so my wiring may be incorrect in some way.

I too am going directly from the 9v battery to the 3.3v regulator, with no issues so far.

It really depends how much current you're drawing through the regulator. Even at 100mA you're only wasting maybe half a watt of power, which IMHO the piece of metal on the back should be able to dissipate just fine. Put a motor or something on there, though, and suddenly you have your own miniature space heater.

Another option is a switching regulator, like this.

stamped

The switching regulator looks like a nice piece of kit. I concur on the heat if pulling some decent current. I still remember the first time I touched a TIP41 (home brew H-bridge without heat sinks) after running a couple of DC motors. I can tell you that I never touched one again (when hot) after that little incident

RichardF

Stamped,
I should have noted that heat generation would only be a problem if operating at rated current. I could be wrong, but this type of regulator is met to be heat sinked if operating at max specs. Dropping from 9 to 3.3 volts at 250ma (not sure of the rating of the PE supplied regulators) would require dissipating about 1 1/2 watts. Don't think these regulators will handle that without a heat sink (I could certainly be wrong though). If you do any kind of apps using sensors you are going to need a 5 volt source in addition to the 3.3 volts. As I said, you can use a 5 volt regulator or a 5 cell NiCd/NiMh.
Regards,
Richard

Drone

Hi Bergamot,

Ouch - the 3.3V 1 Amp Dimension Engineering switching regulator you recommended costs $15 each.

Have a look at Texas Instrument's PTH04000W, a 0.9V-3.6V adjustable 3 Amp switching module (3.3V or 5V input), the product page is here.

The PTH04000W costs around $4.50 ea. in large quantity and $6.56 ea. in unit qty (digikey P/N 296-20392-ND).

These regulators have what is called 'Auto-Track', a feature that allows multiple modules to be powered up/down synchronously even if they are handling different voltages. Auto-Track may be useful in motor applications where more than one module may be in-use. These modules come in either surface mount or through-hole 6 pin DIP MOD form-factor. Each is about 19.0mm X 12.5mm X 8.5mm. A 47uF input cap is required, a 47uF output cap is optional.

I'm still searching for an optimal 3.3V 1A-3A switcher module for propeller - any other suggestions are most welcome.

David

QuattroRS4

Drone,
If package is not critical - take a look at this little beauty ... its a DC/DC converter but just look at the specs !

They call it a 'complete switch mode power supply' ...tasty bit of kit.

www.linear.com/ad/micromodule.jsp
Also attached pdf..



Regards,
Quattro

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'Necessity is the mother of invention'

Post Edited (QuattroRS4) : 7/13/2007 4:03:10 AM GMT

Andy Lindsay (Parallax)

Tom,

The most common cause of the symptoms you describe is one or more broken wires. Typically, a wire gets nicked as the sheath is removed when cutting it for tight wiring. Then, bending it gets it ready to break, and it breaks when it gets inserted into the socket. Sometimes, the remaining sheath is still holding it in place so that it doesn't look broken. After a few minutes of operation, the tenuous connection drifts apart.

Broken leads are not out of the question either. For example, there have been two cases with 4.6 V measured at the LM2937 output that were because one of the leads on the regulator output caps were broken during the bend and socket phase. (I have also managed to inadvertently produce this symptom by inserting a capacitor lead into the wrong socket.)

Sometimes a quick continuity check with a meter will unearth one or more broken wires. In other cases, continuity will come and go as the probes are pressed against the sockets since the shape of the board bends slightly. Especially if I examine a wire or two, and they show evidence of having been partially cut when the sheath was removed from an end during tight wiring, I usually remove and examine each wire looking for breaks and replace any questionable wires.

Andy

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Andy Lindsay

Education Department
Parallax, Inc.

Post Edited (Andy Lindsay (Parallax)) : 7/13/2007 11:09:01 AM GMT

Drone

Hi QuattroRS4,

Thanks for bringing up the Linear Tech LTM46XX... parts, I agree, they're impressive, especially for high current apps. I've looked at these parts before but bounced off them initially due to the difficulty handling the package form-factor in prototype. Even a carrier board would be difficult. 1000's qty. price in a Linear press release is around $12 USD ea.; a quick search shows these modules to run around $30 in unit qty. and $18 in 100's. But they're still interesting parts nontheless given the power and size. I need to look further at them though to see if there is a way to synch the start-up/shut-down like the TI module I mentioned previously. This is important in apps that need current to more than one peripheral each drawing more current than one switcher module can provide; to prevent burning stuff out when you power off/on, "distributed/scaleable power" if you will. Last but not least, I need to look more at the transient performance of these Linear modules. I suspect that with in-module magnetics and such a small package there are going to be compromises in energy storage - hence transient load performance. In-summary; given the hard to prototype form-factor and high unit price, I don't think I will put these parts at the top of my list for 1A-3A switcher module options.

I think the thread about these switcher modules is diverging from Tom's original question, perhaps we should start a new Post about this. My apologies Tom.

Best Regards,

David

Post Edited (Drone) : 7/13/2007 3:45:48 PM GMT

Fred Hawkins

Andy Lindsay (Parallax) said...
Tom,

The most common cause of the symptoms you describe is one or more broken wires. Typically, a wire gets nicked as the sheath is removed when cutting it for tight wiring. Then, bending it gets it ready to break, and it breaks when it gets inserted into the socket. Sometimes, the remaining sheath is still holding it in place so that it doesn't look broken. After a few minutes of operation, the tenuous connection drifts apart.

Broken leads are not out of the question either. For example, there have been two cases with 4.6 V measured at the LM2937 output that were because one of the leads on the regulator output caps were broken during the bend and socket phase. (I have also managed to inadvertently produce this symptom by inserting a capacitor lead into the wrong socket.)

Sometimes a quick continuity check with a meter will unearth one or more broken wires. In other cases, continuity will come and go as the probes are pressed against the sockets since the shape of the board bends slightly. Especially if I examine a wire or two, and they show evidence of having been partially cut when the sheath was removed from an end during tight wiring, I usually remove and examine each wire looking for breaks and replace any questionable wires.

Andy

What happens if the capacitors are placed backwards?

Tom Wyckoff

Andy, interesting point about the wires. I initially built the breadboards using the same color wires as the diagrams to make troubleshooting easier. I use a one-handed pinch & pull wire stripper that cost a small fortune 20 years ago, but has never even nicked a wire. I'm replacing the wires anyway with some from a pre-cut package of breadboard wires, the colors are different, but the wires will lay a lot neater. I'm used to dealing with 78XX series of voltage regulators, and they don't really care what capacitors, if any at all, they have on the inputs or outputs, then I'll check the capacitors, just because they look good don't mean one might not be open. While poking around with a meter I noticed the INPUT lead on the propeller clip has something close to three volts on it and it's connected to the send data pin on the propeller. This could mean the propeller chip pulls it low to send data, or it could mean the propeller clip is bad. Can you check that out for me?

Tom Wyckoff

Update:
I replaced most of the wires on the breadboard, found 3.3 volts on all the rails and on the chip where needed. Still no-go. Then I installed a new propeller chip and it loaded the program from the eeprom and started running. Yay! I have not connected the propeller CLIP yet, see my previous post for a question about that. The last thing I want to do is smoke another $13 chip.
I did notice that the ground side of the capacitor on the output of the 3.3 volt regulator takes a somewhat circuitious route to ground, passing through three jumpers. Maybe a shorter path couls be found for something this critical?
Anyway, if someone could answer the question in my last post regarding the voltage I found on the data input lead of the propeller CLIP I can proceed.
To repeat, I found around 3 volts at the INPUT pin of the propeller CLIP, this is connected to an output on the propeller chip and seems unusual, unless that output is an open collector and pulls the CLIP input low to communicate?

Fred Hawkins

Tom,
This is not a technical answer, just an observation. Which is, when I have my board powered down but still connected to my pc through the plug, the board's power on
led lights about 50% of its usual battery powered state. So, having a plus voltage there does seem to make sense.

As to your cap question -- check out my alternative layout (at least as far as the power is concerned). It is in the Setting and Testing discussion thread:

http://forums.parallax.com/forums/default.aspx?f=25&p=2&m=147808

Fred

Tom Wyckoff

The alternate layout looks like a good idea. I had thought of an off-board power supply, built on one of the dual voltage boards Schmartboard sells, I even have one that I use with Freescale's HC9S08's. But it's all working now. I got brave and tried the propeller clip with a 10k resistor in the TX data line, thinking that would protect the propeller chip. It works just fine so I left it. The bottom line is I smoked one propeller chip, I have no idea how, but if another one goes then for sure I'm going with the off-board power supply.

Thanks to all for the assistance here.

buffler

Gosh, doesn't the 5v regulator use a silicon series pass transistor? So, 2 vbe's are needed plus 5 volts or 7.8 volts at the input, 8 to be sure. The 9v transistor batteries have lousy voltage curves, and lose that first volt pretty fast under load. I just use 12 volts and on some boards have to put a little thermal mass on the 5v reg.
Don

Beau Schwabe

buffler,

The LM2940(5V) is a low dropout regulator only requiring 1 vbe.

http://cache.national.com/ds/LM/LM2940.pdf

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.