PBP projects for R/C models

[Kenjones1935]

My PICkit 2 PORTB outputs do not consistently pull up the coils in the DPDT relays enough to activate them.

The 16F887 outputs measure 2.8v to 3v when driving a coil. I did not find mention of this potential problem in the PICkit2 Manual.. Any ideas anyone?

Is there another Microchip kit that has some output drivers?

Ken

[rmteo]

According to the data sheet, the output high voltage is VDD-0.7 (4.3V with 5V supply) when sourcing 3mA. The absolute max. current sourced/sunk by any I/O pin is 25mA. What does your relay require to activate?

[Kenjones1935]

My ZETTLER AZ8222-2C-5DSE spec says:
Nominal Coil VDC 5 volts
Coil Resistance 125 ohms
Must Operate VDC 3.8 volts.

3.8/125 = 30ma

One relay works out of six when driven by a PORTB output.

NUTS!

Ken

[rmteo]

The current being drawn by the relays is pulling down the voltage to <3V. You need to use a driver (or low VceSat transistor or logic level MOSFET).

[Byte_Butcher]

Keep in mind also that even though each port pin is rated at 25mA maximum, the maximum TOTAL rated current into Vdd or out of Vss is only 95mA.

So even if your relays only draw 20mA, which is within the limits of each port, you could only run 4 of them at once without exceeding the TOTAL current draw through Vdd, because of the 95mA limit.

Like RMTEO said... some nice logic level MOSFETS on the low side of your relay coil is what you need now...


steve

[Kenjones1935]

Does MICROCHIP make an auxiliary board that contains drivers for the PICkit 2 device? I am not capable of soldering onto that PICkit printed circuit board. I already have a good sized non-solder proto board carrying the four DPDT switches, two proximity sensors and a voltage regulator. I am trying to get this whole thing onto a 1/10 scale radio control car.

The guy from whom this idea came used a PICAXE.

Ken

[Kenjones1935]

There are more logic level MOSFET's than Carter has Liver Pills (an expression that easily shows my age).

What I want to do must be very standard.

Suggestions?

Ken

[mackrackit]

http://www.fairchildsemi.com/ds/FD%2FFDD8424H.pdf
I find these handy. Mouser has them.