My other PIR multisensor, on coin cell
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@scalz, may i ask why you choose to use a MOSFET to control the PIR sensor rather than a Bipolar Junction Transistor?
From what i understand, a BJT is normally more favored in lower power circuits, but i may be wrong. You got me thinking here so i went and done a little research this morning and stumbled on this webpage. It shows a table around half way down the page comparing the two devices. I'm still thinking maybe i should use a BJT transistor and its simply just a fact that you prefer working with the MOSFETs.
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@samuel235 your link is right, you should understand the opposite you think in fact..mosfets are field effect in voltage which don't need current on the Gate to enable it, so no power consumption compared to BJT which works in the opposite way and need some current to enable it. And if you take a very low Rdson mosfet and use little current in your circuit there will be almost no lost (and no heat too). Which is one of the explanation for the mosfet acting like a reverse protection, near the batt on my circuit too (because it's very low rdson, + small current drain -> better than a diode which can have some voltage drop). But sometimes BJT are useful too, but not my case here. Another note is on my schem I removed the resistor in serie between gate and atmel (in theory it's better to have one, but depending of the application, you can remove it. Or put a 0ohm in case..).
I'm not a teacher at all but like to share, and with my "english", not easy to translate my thoughts lol! Hope this will help some. True, there are few interesting concept in this schem why I posted it :)
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Does someone have a thought on this??
I am thinking that maybe a 4layer could be better for performance. I already designed few simple 4layer. For RF, even if it can be done&tuned on a 2layer (which require more skills), I still think (maybe I'm wrong) that performance is better on a 4layer. Plus it's easier to match impedance. And finally, but not the smallest pros, that ease your life during routing.
Why I am thinking to this here:
- I could have a whole gnd plane, still better for our antenna whip. But not a big deal here I think, as rfm69 is already good, and I have tried to have a good gnd plane near antenna.
- due to the high impedance paths in the circuit, that needs more care on analog trace, 4layer could improve the routing. Vias for some power supply, some via for gnd, and more room and gnd around analog trace + impedance of the board...I would do 1:Signals, 2: full Gnd, 3: Power traces with gnd maybe, 4:signals.
- have all chance on my side instead of ordering a pcb and then having some troubles...
Cons:
- Need to be sure of my design - > a little bit more expensive for a proto. 24$ for 10pcbs 5x5cm. not so bad if I can get 2 boards on a 5x5, but still a little bit more. To reduce cost that would implie I try to fit this on a 24x49 to have 2 boards on 5x5. And I would have to move some passives on bottom..maybe not a big deal here but I wanted to keep everything on top..and maybe remove programming connector for pogopins.
So it's a small dilemma I thought yesterday...what do you think? I like quality...and the often unbeaten adage says "you have what you pay for"..
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@samuel235 your link is right, you should understand the opposite you think in fact..mosfets are field effect in voltage which don't need current on the Gate to enable it, so no power consumption compared to BJT which works in the opposite way and need some current to enable it. And if you take a very low Rdson mosfet and use little current in your circuit there will be almost no lost (and no heat too). Which is one of the explanation for the mosfet acting like a reverse protection, near the batt on my circuit too (because it's very low rdson, + small current drain -> better than a diode which can have some voltage drop). But sometimes BJT are useful too, but not my case here. Another note is on my schem I removed the resistor in serie between gate and atmel (in theory it's better to have one, but depending of the application, you can remove it. Or put a 0ohm in case..).
I'm not a teacher at all but like to share, and with my "english", not easy to translate my thoughts lol! Hope this will help some. True, there are few interesting concept in this schem why I posted it :)
@scalz, i'm sorry, i should have acknowledged the fact i understand the low current needs of a mosfet compared to a BJT and how that wouldn't effect my mains powered module. But from the research that i have done i can't really see a reason to choose one over the other and for that reason i think i may go with a MOSFET simply incase i decide to swap to a batt for some reason. One less thing to change. The price is slightly more on a MOSFET compared but we're talking very small when its just one or two per device.
Would you still choose a MOSFET for mains powering?
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@Samuel235 humm..sorry maybe I don't understand well what you want to do..AC, battery?? be careful with AC. So what you want to do with bjt or mosfet, depends on your application. With a schematic that would be easier to understand/help you. We or I can't tell you connect this bjt/mosfet like this or like this without seeing what it implie..
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@Samuel235 humm..sorry maybe I don't understand well what you want to do..AC, battery?? be careful with AC. So what you want to do with bjt or mosfet, depends on your application. With a schematic that would be easier to understand/help you. We or I can't tell you connect this bjt/mosfet like this or like this without seeing what it implie..
@scalz I will be converting 240VAC to 5VDC on board and then i want to have a 'switch enabled motion circuit' so using either a MOSFET or a BJT Transistor to switch the motion module on and off. I think that the MOSFET is the best as you provide me with this information concerning the 'advantages' of a the MOSFET.
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I would gladly pay for several of these boards if possible to buy with all components soldered. Any chance of that happening? What would the price /board be in that case?
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@Samuel235 ok that should work. for price, I often use CJ2305 (8v rated) or si2323ds (20v). These are low rdson and cheap at aliexpress. Si2323 is a little bit better
@Cliff-Karlsson thx for your interest. I guess, once the circuit checked, and as there is no exotic chip, that should not be a big deal for the fabhouse I use. They can run small batch if needed. I should check the bom cost too!
Edit: I have looked briefly at the bom, that might cost to me: 25euros/unit. Without thinking my time and big component lot. Maybe cost could be reduced a little bit by ordering more component. My calculation is based on mouser and aliexpress. Most passives at mouser for quality, and not big difference at ali, it depends which one.
What kill the cost is the sensor+rf part: opt3001+si7021+LHI968+rfm69. Rfm69cw and lhi968 at ali, for the rest mouser. Buying sensors at ali will not change a lot the price. If i wanted to use sensors breakout and stack on it, arduino style, that would not make a big cost change and that would kill the thickness..The price to pay to have a complete thing...not a simple arduino board.. -
Ok, just a question, is rfm69cw compatible with rfm69(h)w? And what frequencies do you plan to use?
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@Cliff-Karlsson
All rfm69x are software compatible, work with the same lib. Just the footprint or size which change that's all. I'm not planning to use 433..maybe on a Lora node that would make more sense but if I remember right 433mhz is something regulated..I live in Europe, and for residential use, we have to use 868Mhz frequency. And for example, 915mhz for US.
When ordering radio modules, you have to tell the seller which frequency. If you forget, he should ask you, but better to ask for this during your order. Then, you can set in mysensors, which frequency you want to use. And cut the Wire antenna at the right length (86mm for 868mhz, 82mm for 915mhz). Use a monopole wire (not those with multiple inside). You can coil it (less db but rfm69 is still very good) or if you don't care, let it straight ->more db and range.
It can be better to solder the antenna directly to the module on antenna pad/hole. Here for instance I have added a hole on pcb, sticked to the antenna pad. It's ok. But sometimes you can see on other boards (I did this too) where the antenna pad is not near. the routing if not well done can detune a little the antenna and have less range. -
@scalz, could you just confirm to me that your PIR circuit is working with the P-Channel MOSFET please?
I'm attempting to get a P-Channel MOSFET in the UK and i just can't source 1 MOSFET below £10. Which, honestly is ridiculous, if i know that your sensor is working as intended I will just design my circuit like this and know it will work without any prototyping.
However, I'm using the motion module (HC-SR501) and propose to have it setup like normal however, i would have my P-Channel MOSFET on the 5V VCC line and switch it using a digital pin.
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@scalz said:
si2323ds
SI1869DH is also worth a look as a very nice, general purpose load switch (low volts all the way up to 20v).
@NeverDie said:
@scalz said:
si2323ds
SI1869DH is also worth a look as a very nice, general purpose load switch (low volts all the way up to 20v).
Not sure why my find function never picked this up to be honest. Thank you for point it out to me, much appreciated :)
Would still like to know if Scalz has this board in working order with the schematic shown.
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@NeverDie thx. I know this sensor. a bit thick. And I had others goals! thin and compact overall with custom box, I like custom box, you can think your assembly, and it's durable source (stl),
for sharing some parts, and fun a to z training/challenge :)@Samuel235 not yet. I have received pcb some days ago. but I'm missing few values to assemble pir. I delayed a bit my order because I have other board/bom, and try to have free shipping each time ;)
but I already use p mosfet on other sensors boards and that works nice...
true, I could have shown you what looks my pcb..so it's white because box will be white and with transparency, I don't want to see the board. But I noticed that each time silkscreen never looks good on white...few ugly things but that will be tiny and thin I think ! I can't wait to assemble it and debug it :)
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@NeverDie thx. I know this sensor. a bit thick. And I had others goals! thin and compact overall with custom box, I like custom box, you can think your assembly, and it's durable source (stl),
for sharing some parts, and fun a to z training/challenge :)@Samuel235 not yet. I have received pcb some days ago. but I'm missing few values to assemble pir. I delayed a bit my order because I have other board/bom, and try to have free shipping each time ;)
but I already use p mosfet on other sensors boards and that works nice...
true, I could have shown you what looks my pcb..so it's white because box will be white and with transparency, I don't want to see the board. But I noticed that each time silkscreen never looks good on white...few ugly things but that will be tiny and thin I think ! I can't wait to assemble it and debug it :)
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I love!
I was reading the other day about using White silkscreen layer on top, and then the names and values where on the top copper layer (being very careful), it gave the effect of pure white and gold plated. It looked beautiful!
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@scalz - Could you take 2 minutes to check this MOSFET for me please, do you think this would work in our application? Once i get the board made i will be using the exact one you have, but i need to breadboard all of this together to learn.
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@samuel235 I think you don't need a 17amp mosfet.. for breadboarding, you could use the common TO92 BS250 instead. just a thought :)
