Post by thread:PIC project with lots of vibration

Have a shaking application, where the PIC chip will be mounted on a piece of machinery that's vibrating. A lot. And am talking to someone making a rocket telemetry unit in future using a PIC chip. I'd sort of LIKE to socket this PIC chip, past experience (sumo robots etc.) has been that IC's tend to do spurious resets from short Vcc dropouts, etc. as the socket connectors bounce away from the IC pins, when these robots collide. I suggested soldering the MOT cpu in for this particular app., seems my advice was good =) Anyone here know what type of sockets are best for vibration-type environments? In future I'll be doing TOO much shaking applications, some rocketry telemetry (I hope!) included. I'd think an Augat would be pretty good (multi-prong machined pin socket.) I've thought of using a ZIF socket, even though expensive they're pretty solidly contacted. Or is solder just THE best here? (With /JW parts, versus flash parts, things have changed to where soldering is not as bad of a pain as it once was, with ICSP being available!) Nice to avoid soldering if I can, though. One cheat for when you know there'll be socket drop-outs or power faults: Hard solder a cap or two across the uController, and perhaps do the same for your pull-up resistor for !MClr - that tends to reduce problems. (But: it's a pain!) Mark

Mark Willis wrote: {Quote hidden}> > Have a shaking application, where the PIC chip will be mounted on a > piece of machinery that's vibrating. A lot. And am talking to someone > making a rocket telemetry unit in future using a PIC chip. > > I'd sort of LIKE to socket this PIC chip, past experience (sumo robots > etc.) has been that IC's tend to do spurious resets from short Vcc > dropouts, etc. as the socket connectors bounce away from the IC pins, > when these robots collide. I suggested soldering the MOT cpu in for > this particular app., seems my advice was good =) > > Anyone here know what type of sockets are best for vibration-type > environments? In future I'll be doing TOO much shaking applications, > some rocketry telemetry (I hope!) included. I'd think an Augat would be > pretty good (multi-prong machined pin socket.) I've thought of using a > ZIF socket, even though expensive they're pretty solidly contacted. Or > is solder just THE best here? (With /JW parts, versus flash parts, > things have changed to where soldering is not as bad of a pain as it > once was, with ICSP being available!) Nice to avoid soldering if I can, > though. > > One cheat for when you know there'll be socket drop-outs or power > faults: Hard solder a cap or two across the uController, and perhaps do > the same for your pull-up resistor for !MClr - that tends to reduce > problems. (But: it's a pain!) > > Mark Mark, I had some experience with electronics in Racing Car environment. Just to you have an idea about vibration, some drivers need to replace their dental fillings quite often (specially when they hit the wall... hehe). There are two ways to protect electronics: a) create a cushion system for each sensible component, or b) tied as firmly as possible that component to the pcb. It sounds crazy, but sometimes cushion means broken leads, some components just got ripped of from the board. It is not difficult to find out some DIP 14 chips with two or more broken legs, not even talking about circuit board thin tracks just cracked or floating in the air. Missing smt resistors and capacitors is not rare. The best thing to do is find out the vibration frequency and look for the best cushion system for that particular frequency. A complete different cushion is required for a V-8 or V-12 cylinders engine racing car. A tick resin covering all components (epoxy or araldite) is what you can find in some surplus boards, clearly sold somehow from military crafts. Forget about maintenance. Circuit board and tracks should be as tick as possible, sometimes with a metallic frame to keep it straight. If you really need sockets, the machined golden ones with an extra chip holding clip would be a must. I would go for Flash devices that can be on board programmable, avoiding sockets at any cost. Use several small power capacitors around the board instead single big one. Silicon glue all crystals parallel to the board, with "S" leads shape to avoid problems. Just to have an idea what it is, just drop 10 ice cubes into the blender and turn it on at max speed, imagine your circuit right there, close to the blades, and think about which part will break first. It is a complete new world.

At 01:20 PM 9/27/99 -0700, you wrote: >Have a shaking application, where the PIC chip will be mounted on a >piece of machinery that's vibrating. A lot. And am talking to someone >making a rocket telemetry unit in future using a PIC chip. biiig snip Got three Pics plus sRAM and ADC and signal conditioning with four accelerometers, three strain gages, and a rate sensor in two cubic inches, three pcb's in cord wood packaging, surviving 500 G impacts. NOT socketed! All SMT and firmly soldered in place. Trick is to dip first into GE-RTV silicone rubber (real watery, clear, self releasing two part stuff) to provide an easily removable conformal coating. Let it cure, then pot with a urethane or epoxy filled with micro-balloons (syntactic foam filler) for strength and light weight. Whole package is pretty much indestructible--and can still be taken apart for repair or failure analysis. kelly William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems <spam_OUTborsumTakeThisOuTdascor.com> & <http://www.dascor.com>San Diego, California, USA

I used to work for a company that made train mounted equipment. It involved two fully duplicated systems, with several micros, dsp's and a whole load of firmware. Firmware updates were fairly frequent during the development phase so socketed eproms were needed. We soldered the eproms into turned pin DIL headers (the type with the solder buckets) and these were plugged into turned pin DIL sockets (all gold plated type). There was enough room under the socket to fit a small nylon tie wrap which held the whole assembley pretty secure. We had no problems, but the resulting arrangement could hardly be called "low profile" Regards Mike Rigby-Jones > {Original Message removed}

At 08:52 AM 9/28/99 +0100, you wrote: >I used to work for a company that made train mounted equipment. It involved >two fully duplicated systems, with several micros, dsp's and a whole load of >firmware. Firmware updates were fairly frequent during the development >phase so socketed eproms were needed. We soldered the eproms into turned >pin DIL headers (the type with the solder buckets) and these were plugged >into turned pin DIL sockets (all gold plated type). There was enough room >under the socket to fit a small nylon tie wrap which held the whole >assembley pretty secure. We had no problems, but the resulting arrangement >could hardly be called "low profile" Had another thought on this subject.... It used to be possible to buy just the machined fingers from standard sockets. The holes in the PCB were held to fairly tight tolerances and the fingers were press-fit directly into the holes. Thus, the PCB itself became the socket. Once all the debug and burn-in was complete--with the socketed parts easily replaceable--the board was wave soldered. Kelly William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems <.....borsumKILLspam@spam@dascor.com> & <http://www.dascor.com>San Diego, California, USA

> Had another thought on this subject.... > It used to be possible to buy just the machined fingers from standard > sockets. The holes in the PCB were held to fairly tight tolerances and the > fingers were press-fit directly into the holes. Thus, the PCB itself > became the socket. Once all the debug and burn-in was complete--with the > socketed parts easily replaceable--the board was wave soldered. > > Kelly Do you know that exist that kind of sockets to be attached directly to the pcb holes? Yes, even that it allows a low profile pcb, they are expensive. For sure you can destroy some machined sockets and use just the "fingers" to do it, but the main gain here is the low profile. The problem with the socket connection for high vibration is between the "finger" and the component lead (mechanical stress), not between the "finger" and the soldered PCB hole. Wagner

>Had another thought on this subject.... >It used to be possible to buy just the machined fingers from standard >sockets. The holes in the PCB were held to fairly tight tolerances and the Yes, this is still possible. You can get them from MilMax. My contact for them is Mike Rosen mrosenKILLspamhome.com Andy ================================================================== Eternity is only a heartbeat away - are you ready? Ask me how! ------------------------------------------------------------------ .....andyKILLspam.....rc-hydros.com http://www.rc-hydros.com - Race Boats EraseMEandyspam_OUTTakeThisOuTmontanadesign.com http://www.montanadesign.com - Electronics ==================================================================

I recall that the trade name we used years ago was "holetite" but wouldn't swear to it. Any of the major manufacturer should be able to supply them eg AMP, Samtec, etc. I know I saw them in a catalog that crossed my desk in just the last couple of months. Darned if I can recall whose it was though--not one of the majors--but someone like MilMax or Samtec. Fingers are indeed the problem when vibration exists. There were a few tricks to the holtites I can pass on if it becomes of serious interest. kelly At 01:34 PM 9/28/99 -0400, you wrote: {Quote hidden}>> Had another thought on this subject.... >> It used to be possible to buy just the machined fingers from standard >> sockets. The holes in the PCB were held to fairly tight tolerances and the >> fingers were press-fit directly into the holes. Thus, the PCB itself >> became the socket. Once all the debug and burn-in was complete--with the >> socketed parts easily replaceable--the board was wave soldered. >> >> Kelly > >Do you know that exist that kind of sockets to be attached directly to >the pcb holes? >Yes, even that it allows a low profile pcb, they are expensive. For sure >you can destroy some machined sockets and use just the "fingers" to do >it, but the main gain here is the low profile. The problem with the >socket connection for high vibration is between the "finger" and the >component lead (mechanical stress), not between the "finger" and the >soldered PCB hole. > >Wagner > > William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems <borsumspam_OUTdascor.com> & <http://www.dascor.com>San Diego, California, USA