Trying to fix manufactures problem.

[ProjectBox]

Trying to fix a automotive Bluetooth mute circuit that will not trigger a automotive relay.
The unit output is very high impedance - 1meg so I try is a simple relay driver with a TIP42 PNP (all I had laying around at the shop). This seem to work, but some times not release the relay. So try put a 1K on the base but this will not trigger relay.
I contacted the manufactures tech and they recommend a reed relay to trigger the automotive relay. As I read reed relay I cringed for fear of it locking up or worse in the bumpy car ride, triggering randomly.
So if any one help a guy out, I would much appreciate it.
I can build anything if given instructions.
Almost forgot the coil is about 90ohms on the automotive relay
**broken link removed**

 

[4pyros]

Reed relays are not any more sensitve to bumps than automotive relays. the little wires used in them will only move with a magnet, you can not bump them on.

 

[Boncuk]

Hi,

the TIP142 is an NPN-darlington transistor and you used the wrong symbol for it.

The transistor to be used should be a PNP-darlington transistor, such as the TIP145 (TIP146 and TIP147)

I doubt that the base current will be high enough to saturate a PNP darlington. It can stand a collector current of 10A!

Why not use a P-channel MosFet like the BS250 to drive your relay? The gate voltage has to be low in order to make it switch and uses almost no current.

Boncuk

 

[mvs sarma]

suspect the added resistor of 1K might be an open or developed high resistance
.