Inverting Pulses Circuit - Need Help.

Lookup H-bridge driver ICs. These contain four switches and are often used to drive small motors, etc. You should be able to find a single IC that can be controlled by a PIC output pin. There are also lots of simple discrete-part circuits on the web, but some are not as good as others. Do you know what the DC resistance of your solenoid is?

I will look for the H-bridge... the DC Resistance is about 42 ohms.

Thanks for the tips!

Rickydou

Maby your idea isn't that bad, but you might be using the wrong type of relay. The following is taken from

:

Make-before-break, break-before-make

In a multi-throw switch, there are two possible transient behaviors as you move from one position to another. In some switch designs, the new contact is made before the old contact is broken. This is known as make-before-break, and ensures that the moving contact never sees an open circuit. The alternative is break-before-make, where the old contact is broken before the new one is made. This ensures that the two fixed contacts are never shorted to each other. Both types of design are in common use, for different applications.

Did you wire your relay as a crossover? Unless it's a make-before-break type, a crossover shouldn't give you any intermediate shorts.

+V o--------+-----------o | \\_______________ out 1 | +------o | | | | -V o--------)----+------o nc | \\_______________ out 2 +-----------o no

(note the "no connect" ')')

Good Luck! Rich

OK. Allegro is an IC company that makes lots of H-bridge or "bridging" ICs. A common use for these is to drive stepping motors, and these have two windings, each of which needs to have reversible current polarities. That means the ICs have two H-bridge outputs. These ICs have lots of pins, but they usually come in small IC high-density surface-mount packages. We'll not give these ICs any further attention.

A few older ICs, such as the A3953SB, have only one H-bridge and come in DIP packages, which is better suited for hand- wired prototyping. DigiKey has these for $3, p/n 620-1065-ND, datasheet at

This part is spec'd to work well down to 5V supplies, but we must say that since it's meant to work to 1.3A, it uses Darlington and complementary Darlington (Sziklai, see AoE page 95) output stages. These eat up over a volt at 120mA, and reduce the drive voltage from 6 to 5V when the battery's nearly dead. But if the solenoid can work at 5V, that's OK.

Use TWO DP relays, one wired to apply polarity 1 when closed and a second to apply polarity 2 when closed. The you can switch the two polarities completely independend from each other.

Best regards Ulrich Bangert

schrieb im Newsbeitrag news: snipped-for-privacy@c77g2000hse.googlegroups.com...

power supply decoupling.

Bye. Jasen

Rich, this is exactly what I did the first time. But I bet my relay was a Make Before Break causing the short to happen. I have a hard time finding a 5VDC Coil relay DPDT that is Break Before Make type. Is there another way to call them that is more official that may be in the Specs?

Thanks

Rickydou

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Thank you Ulrich, This was my PLAN B... I was just looking for a solution that was requiring less Relay... But it might come out as the easiest answers!

thanks

Rickydou

The thing you might be missing is that the solenoid has inductance, which causes a high voltage flyback every time it is de-energised. Most relays do have what is called a Common Open Time (COT), but if a set of opening contacts arc due to the flyback voltage then everything probably gets shorted in there.

The trick is to clamp the flyback voltage to a safe level and to dry switch the relay. Modified sketch below.

+9 o--+-----+-----------o _|_ | \\________ Clamp /_\\ | +------o ___|____ Diode | | | | | | | | |Solenoid| +-----)----+------o nc |________| 10mS | | \\________| _ |/ +-----------o no | | -/\\/\\--|Q1 /|\\ _| |_ |> __|_ --+--9v Pulse | | | | --+--0v +---|Coil|-----+ | |____| | | | .------------+----|>|-------+ | Direction |/ Logic -/\\/\\--|Q2 Level |>

| --+--0v

1. Q1= OFF. Set Q2 ON or OFF for direction, as req'd.
2. Pulse Q1= ON for 10mS, then OFF.
3. Set Q2= OFF, (just to save power).

This means that the direction relay is only moved when the solenoid is unpowered.

--
Tony Williams.