St7 burned out?

[marco32]

Posted on October 08, 2003 at 05:47

St7 burned out?

[marco32]

Posted on October 07, 2003 at 08:58

Hello St freaks,

My uC is burned out for the second time?? It happends by programming the uC. By programming the uC the relay (The relay is powering an 230Vac valve) will switching with a frequency of +/- 10Hz. I think he don't like spikes in the air!! The pcb have a ground layer. The incomming power is 2x9Vac. There are a lot of wires to the pcb, but all of them are grounded Has anybody suggestions, to improve the pcb? Does anybody know where i can buy 56 sdip IC-feets? You never know howmany times i must replace the uC![ This message was edited by: Moppie on 07-10-2003 12:29 ]

[peterharris9]

Posted on October 07, 2003 at 22:30

Hi There

Assuming you have all the basics for a micro circuit in place: capacitors on all supply lines, unused pins pulled up/down, clock connections as short as possible etc. Driving a relay should be straight forward. Make sure you have a diode across the relay coil to deal with the back EMF when you switch the relay off. Make sure the micro can deal with the relay current, you may need an external transistor to switch the relay. If you still have problems, try a series resistor/capacitor ''snubber'' circuit across the relay contacts. BM [ This message was edited by: Battman on 08-10-2003 02:07 ]

[marco32]

Posted on October 08, 2003 at 05:47

Thanks for reply,

On the PCB there is for every IC an capacitor of 10nF Clock lines are very short. The ISP lines are longer to connect with the ISP connector, but short as possible. (I use the ST72334N4B6, sdip56) The reset line in the ground layer Unused pins are defined as push/pull output There is an diode across the relay coil. Also the relay is driven by an relay driver I don,t have a snubber circuit. It's a good idea! But the ST7 don't like the spikes. Before the ST7, i use the ST6 and i've never got these problems Is the ST7 more sensitive for these spikes or something? Or do i something wrong? Anybody other suggestions?[ This message was edited by: Moppie on 08-10-2003 09:18 ]