View Full Version : Fried 3 Basic Stamps and need help!
01-22-2007, 10:53 AM
I've been building a thermostatic controller using the BS2pe.· It uses a M41t0 clock on pins 1-2 (no resistor).· Pin 3 is a serial LCD (no resistor).· Pin 4&5 are buttons(using traditional pull up resistors).· Pin 12-15 are relay outputs (protected by 1k resistor).· Worked great on protoboard, been working for weeks on a permanent board I made.· Permanent board is·a ebay kit·I bought (ph anderson I think) with a built in serial·and 7805 vreg.· Suddenly it dies...the BS2pe chip gets super hot and the current draw goes from 100 to 300+ ma.· BS2pe dead, no response on my protoboard.· I check for shorts, disconnect some inputs, retest it with my BS2p.· It dies, same symptoms, won't respond, gets hot.· I look again for shorts, decide to disconnect inputs and increase io resistors.· Connect my spare BS2p, works for awhile, then dies same overheating.· Now that I'm out $225+ in basic stamps I'm ready to trash my protoboard, start over·and switch to $5 pics.· Sorry, just frustrated:)· I've been using stamps for over a year, been doing electronics for years and i'm very upset about this problem.· I've looked· for shorts in every way I know of and don't know how to proceed.· I know·some of you may want a schematic, which I don't have since I copied the wiring from my parallax proto board.· Just hoping for a·quick tip, but can hand·draw a schematic if required.· Thanks·anyone, I really am considering abandoning stamps out of frustration and·cost!···
01-22-2007, 11:05 AM
Well , I would be considering drag your permanent kit ! .. please , draw us a schematic. anything that could clarify your ploblem. ( as you do draw the schematic , you will probably fnd the problem )
I would like to help, but need more information
01-22-2007, 12:18 PM
I found that the 7805 voltage regulator on the P.H. Anderson board is capable, and has a tendency to lean back and short out the pins on the BS2. Literally. (It was the cause of blowing a few stamps myself.) It took a while but I did figure it out when I got lucky and caught a spark out of the corner of my eye. Apparently, when I pushed the cover on the project box closed it would push the regulator over just enough to cause a short. To make matters worse, it would pop back up when I took the cover off, so I simply couldn’t figure out what was happening? And yes things got very hot including my temper!
I was getting very frustrated and unjustifiably blamed the stamp. I simply put an insulator behind the regulator to prevent it from shorting the pins out and haven’t had a problem since.
Perhaps something like this is what is happening to you?
Post Edited (jhoyoza) : 1/22/2007 6:39:26 AM GMT
01-22-2007, 12:45 PM
Why not try to troubleshoot what you have left? See where there is voltage and where there is none. Check the voltage levels against what you expect them to be. Start at the "source" (battery or wall wart) and proceed forward through the circuits until you find something amiss.
01-22-2007, 02:51 PM
That's a tough hit with Stamp Modules. You could save some money with them by purchasing the OEM components and building them into your circuit.
Another good, lower cost solution, is the SX Protoboards. The boards are only $10, an SX-Key is $50, and the SX-B compiler is free.
SX/B isn't that much more difficult than PBasic, and the learning material is starting to become more readily available. There should be some books out soon, and John Williams has been writing about SX/B in Nuts & Volts for awhile.
Here's a link to the protoboards: www.parallax.com/sx/sx_products_overview.asp (http://www.parallax.com/sx/sx_products_overview.asp)
01-22-2007, 09:53 PM
Without seeing your circuit or schematic, this is only speculation. You describe Pin 12-15 as "relay outputs (protected by 1k resistor)". Are these pins controlling relays, and, if so, are they using driver circuitry and also "protected" by diodes across the relay coils to prevent back-EMF? (This subject is covered in the WAM text as well as elsewhere in these fora.) Normally, without these diodes I would only expect the pin drivers to fail, but who knows...
Again, more info about your circuit would help in the diagnosis...
Truly Understand the Fundamentals and the Path will be so much easier...
01-23-2007, 09:31 AM
You may be right.· As i was trying to diagnose, (a risky move with my last BS2 chip) i noticed the display flickered when I bumped the 7805 VR.· Especially since the last thing I did before disaster was add a small heat sink as the VR was getting pretty hot.· I noticed the middle pin of the 7805 was loose (from the force of mounting the heatsink) when I wiggle it, the power led gets bright and the serial lcd goes crazy.· I'm not sure if this is it as I don't understand how a loose connection on the 7805 can cause b+ to spike, but i'm not an engineer (any engineers here?).· It seems to be working so I'll keep testing.· I put an insulator on the heat sink just in case.
Tom,·pins 12-15 go to a 1k resistor which feeds a relay board (another ebay purchase) that uses transistor drivers with reverse diode protected relays.·
Also forgot to mention that pin 6 drive an array of 4 single wire DS18b20 temp sensors.
If this isn't it I send a schematic and a prayer.· Thanks for the tips thus far.
Phil Pilgrim (PhiPi)
01-23-2007, 10:10 AM
An unconnected ground pin on your 7805 will allow the input voltage to pass through to the output, attenuated only by the regulator's dropout voltage which, for the 7805, is around 1.5V.
·You'll have the same failures even if you use a 5 dollar PIC processor, besides you will still need a 100 dollar or so compiler with the·pic.
·Vertically·mounted unsupported regulators·are ticking time bombs for electronic circuits.
··When the middle lead broke loose from the circuit You lost your ground connection and hence your regulation of 5 volts.·
·The regulator output·voltage·will rise above 5 volts thereby blowing your stamp and any other IC's running off of 5 volts max.
You really should mount the regulator·horizontally·to a PWB with the leads bent, but do not bend the leads right at the body/case otherwise they will eventually crack and your problem will repeat itself once again.· Put a mounting screw thru the tab hole, thats what·the tab hole was made for.
Have you ever seen a Parallax Board of education board ?· If not then check parallax and find a picture of one, that's how the regulator should be attached.·
01-24-2007, 07:22 AM
Glad to help!
I found parallax products to be outstanding! And despite 'wanted-dead-or-alive-posters' covering the walls of customer support center with my 'puss' on it, they all have been wonderful, and exceptionally patient in providing beginners, like myself, with dedicated support.
Heck, if it wasn't challenging, it wouldn't be any fun now would it? I'm kidding about the posters of course.
(Don't tell them, but Customer support was right on the money when it came to figuring out my "buy-'em-and-fry-'em" problems...it just took a while for me to understand what it was I was doing wrong.)
I feel honored to have the opportunity to share some of my findings (or lets say disasters) with others, as so many of you have been so helpful to me! I wonder if P.H. Anderson is aware of the regulator issue? It wouldn't break my heart if Parallax used the hefty 7805 as they are one tough regulator and recover nicely from overheating and shorting out.
01-24-2007, 10:21 AM
Just wanted to say thanks for the regulator tips from everyone, this is a great community made possible by people volunteering their time.· I'm about 95% confident a the loose pin or grounded heat sink is the problem.· Regretably there is no room to surfacemount the VR on the PH Anderson proto board.· As for me, I've never lost faith in the BS technology, but blowing 3 in one day at it's price point is enough to make be consider pics.· Now that my BS inventory is fried, I'll order a·SX·and consider porting my app.· Time to try something new.· Thanks again guys and I'll be back if this isn't the problem.
01-24-2007, 10:40 AM
Send me your shipping address firstname.lastname@example.org and I'll get you an SX programming tool to get started.