Realised that after I posted so thanks for removing. I couldn't see a method for sending PMs though, can you point me in the right direction?MOD NOTE: Don't put e-mail addresses is posts or your public profile. It's guaranteed to attract spambots looking for targets. Instead, ask people to PM you (i.e., start a Conversation with you).
Look in the upper right (if you are using the Blue schema) and you will see "Inbox". Select that and you should see something that says "Start a conversation" or something like that.Realised that after I posted so thanks for removing. I couldn't see a method for sending PMs though, can you point me in the right direction?
Cheers
Nick
Hi AlecYou're right.
I think you already have a PFET? (It needs to be one with a low Vgs(thr) value). As for NFETs, there are hundreds to choose from. Try a parametric search on the web-site of any stockist (e.g. Digikey, RS, Farnell). Look for something with a Vgs(thr) value <1.5V and a Rds(on) value <20mΩ.
Simulation says not, since there's no significant voltage spike.
They'll do nicely.
Edit: M1 is a PFET, M2 is a NFET.
These 2 might be better. They need to be what they call logic level, so they will work on 6 volts.Hi Alec
Just wondered if you'd mind casting your eye over my selection of FETS for the Dual Polarity Pulser? They've been quite tricky to find and I want to make sure I get the right ones.
PFET:
http://uk.rs-online.com/web/p/mosfet-transistors/7604246/
NFET:
http://uk.rs-online.com/web/p/mosfet-transistors/5429759/
Many thanks
Nick
Many thanks Ron. Components ordered. Will update you and Alec when prototype complete.These 2 might be better. They need to be what they call logic level, so they will work on 6 volts.
This applies to the gate threshold voltage.
The PFET will be a little hard to solder to since they cut the drain lead off, but you can solder to the back.
http://docs-europe.electrocomponents.com/webdocs/11a6/0900766b811a65e9.pdf
http://docs-europe.electrocomponents.com/webdocs/0791/0900766b807913bc.pdf
Hi Alec_tIf you wanted to try a single-coil version with pulse polarity reversal, here's my offering.
The switch would be provided by your RF receiver. A pulse of one polarity is generated when the switch closes and lasts for the shorter of ~0.5sec and the duration of switch closure. When the switch opens, a pulse of the opposite polarity is generated and lasts for ~0.5sec.
View attachment 100327
Standby current drain is zero (plus the RF receiver draw).
Hi Alec_tHi.
An N type FET should work as the switch, provided the RF receiver can keep the FET on or off continuously for at least the ~0.5 sec required to allow C1 or C2 to fully charge/discharge.
Can you post a schematic of the receiver output stage and how you are interfacing the receiver to the rest of the circuit?
Hi Alec_t, the rating for the receiver is 5 - 10v. Not sure if that's what you mean or am I making a schoolboy error somewhere?There is a supply voltage conflict in your setup: 5V from the receiver is connected directly to 6V from the two batteries in series.
Think I've seen the error of my ways. The Mosfet used for the switch looks like it could be shorting out the power supply to the receiver. Do you think the attached would work or is it close but no cigar?So, you'd run the receiver from the 6V supply.
Many thanks, I'll give it a try this evening.That should work, with the post #89 proviso.
Just hooked it up as per the schema I posted earlier – same result unfortunately. When I press the remote the coil pulls the magnet towards it, when I release there’s no reverse polarity. When I press and hold the remote constantly the coil pulls the magnet towards it and then just pulses. Again no reverse polarity when it’s released. Strange.That should work, with the post #89 proviso.
I’m using AAA cells to power the circuit and receiver. The arrangement is 2 x battery holders each containing 2 x 1.5v cells connected in series as per the configuration in the original schema. AAAs are ideal as they are powerful and small.What are you using as the +-3V supply? It sounds like the coil current may be pulling the voltage down too far for the circuit to work as designed. What is the coil current (or resistance)?
The ground of the separate supply will need to go to ground of the circuit as well (Source of the NFET)I’m using AAA cells to power the circuit and receiver. The arrangement is 2 x battery holders each containing 2 x 1.5v cells connected in series as per the configuration in the original schema. AAAs are ideal as they are powerful and small.
As I mentioned in my original post, space is limited as all this has to fit in wood boxes 9 x 9 x 4cm, so there isn’t really space for a separate power supply for the receiver. My aim was always to use the same power source for the circuit and receiver if poss.
I’m going to hook up the receiver to a separate power supply this evening to see if it makes a difference. I’ll also try and get a read on the current draw of the coil and report back.
Many thanks
Nick
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