reef-pi :: An opensource reef tank controller based on Raspberry Pi.

[Ranjib]

Finally got my ribbon cable, and I'm updating all the software now. I was on reef-pi 1.0 for pi3, now I'm taking it to 2.0, and updating the OS as well. I was unable to add any outlets when I fired everything up, so either the ribbon cable is backward, my db-9 cable is the wrong one, or it simply needed to be updated. I'll know soon enough.

Unfortunately, you have to re-create everything in 2.0

 

[DirtDiggler2823]

Unfortunately, you have to re-create everything in 2.0

I loaded all the software previously when I first started, months ago, but I had no ancillary hardware on the machine until today. I've just added all of the connectors, and I got an error on the J3 rpi jack.

 

[DirtDiggler2823]

Hey, I enabled HTTPS, and now I can't get into the UI at all.

 

[bishoptf]

I can't answer your questions, but I'm jealous that you live close enough to a hobby electronics store to make a trip. The nearest to me is almost an hour away. These are the days I miss Radio Shack.

Yeah I am fortunate to have a local store and its a great store, its near my work which is 30min away but they have anything you could possibly want, Gateway Electronics, see pictures, hard to do it justice but aisle and aisles of stuff! :)

Also attached are my non reef aquariums, nothing near as nice as what you guys have but what I am going to use reefpi for...

 

[bishoptf]

Get few 4.7k resistor, couple of logic level power mosfets for backup

I purchased everything on my list including the mosfets, I think I understand the basic idea of how to hook thinks up, I have a bread board and will use that initially to work things up. I purchased a small proto board that I can transfer things permanently once I have things worked out. Looking at your guide I understand how things are laid out for the most part but not sure about the resistors, if I will need one and if so what size.

If anyone has some thoughts on how to proceed, I would welcome the input. :)

 

[bishoptf]

Looking at the light controller guide on ada fruit I think the actinic LED looks to be the section that I would want to emulate. Would it make sense to use the NPN transistors or use the mosfets. My other question is the resistor that is shown in the Fritz diagram, not sure what value it is, looks like a 10k resistor but not sure. Would the actinic led diagram https://learn.adafruit.com/reef-pi-lighting-controller/circuit-construction be a good starting point to follow for controlling my led lights?

:)

 

[Ranjib]

Looking at the light controller guide on ada fruit I think the actinic LED looks to be the section that I would want to emulate. Would it make sense to use the NPN transistors or use the mosfets. My other question is the resistor that is shown in the Fritz diagram, not sure what value it is, looks like a 10k resistor but not sure. Would the actinic led diagram https://learn.adafruit.com/reef-pi-lighting-controller/circuit-construction be a good starting point to follow for controlling my led lights?

:)

Probably you have already done this, but can you link /share your light details. How you are powering the light? We need to understand the dimming circuit. You mentioned you have a inline dimmer already, can you share an image of that, particularly anything that has technical spec in it

 

[bishoptf]

Probably you have already done this, but can you link /share your light details. How you are powering the light? We need to understand the dimming circuit. You mentioned you have a inline dimmer already, can you share an image of that, particularly anything that has technical spec in it

Its from china, actually the led's are pretty decent, they can put off quite a bit of light, https://www.ebay.com/itm/Chihiros-A...108a15d47:m:mwkmZs_vgGludiBf5ipncvw:rk:3:pf:0 for planted freshwater tanks they are pretty decent, I have a 50CM unit and a 20cm unit. Came with the dimmer jumper and a 12v 5amp power supply, it says 5amps but it's really light, not much weight to it at all so I really doubt it could do 5amps. I finally cut the heat shrink off of the dimmer jumper so you can have a better view. I listed on the previous page what the frequency readings were when going from low to high, it still cycled even on the frequency unless you were at max brightness @12v.

Here are the pictures:

Let me know if I need to get a close picture of something, etc...

 

[Ranjib]

use the logic level mosfet circuit and pass your power through it, i.e. you are not sending a control signal to your light (like we do in kessil, where the light has a separate power source), you are actually controlling the main power source directly. Hence we expect high current draw, and a mosfet is ideal for this

 

[bishoptf]

use the logic level mosfet circuit and pass your power through it, i.e. you are not sending a control signal to your light (like we do in kessil, where the light has a separate power source), you are actually controlling the main power source directly. Hence we expect high current draw, and a mosfet is ideal for this

Correct since when I looked with the meter even though it was cycling the voltage was going down, so that circuit you have for the arctinic circuit would be what I am after, correct? I think you were using it for the moon light and was just an led strip, my only question is what size resistor do you think I should use?

 

[Ranjib]

Correct since when I looked with the meter even though it was cycling the voltage was going down, so that circuit you have for the arctinic circuit would be what I am after, correct? I think you were using it for the moon light and was just an led strip, my only question is what size resistor do you think I should use?

yes. 1K should be good enough. This is a good tutorial on how to use them https://learn.adafruit.com/rgb-led-strips?view=all

 

[bishoptf]

yes. 1K should be good enough. This is a good tutorial on how to use them https://learn.adafruit.com/rgb-led-strips?view=all

That looks like will help, one more question then I am turning in, I'm thinking I probably need beefier mosfets that I purchased, the big led unit has 99 led's in it and the small one has 36 led's. The ones that I purchased today were mosfet 2n7000-h45, based on y initial reading of that article you linked I will probably need a higher rated unit for the bigger unit. I have a kill-a-watt and never hooked it up to see what it pulls at the highest setting, although I will never run it on its highest setting, what size mosfet do you think I will need.

Looks like i will need to go with something like the IRLB8721, would provide plenty of headroom.

 

[Ranjib]

That looks like will help, one more question then I am turning in, I'm thinking I probably need beefier mosfets that I purchased, the big led unit has 99 led's in it and the small one has 36 led's. The ones that I purchased today were mosfet 2n7000-h45, based on y initial reading of that article you linked I will probably need a higher rated unit for the bigger unit. I have a kill-a-watt and never hooked it up to see what it pulls at the highest setting, although I will never run it on its highest setting, what size mosfet do you think I will need.

Looks like i will need to go with something like the IRLB8721, would provide plenty of headroom.

yeah, i think thats not a power mosfet. Logic level power mosfets look beefier, TO-220 packaging instead of TO-92. If you have ULN2803, you can use those as well, they are fairly good till almost 1A, if i recall correctly

 

[Ranjib]

yeah, i think thats not a power mosfet. Logic level power mosfets look beefier, TO-220 packaging instead of TO-92. If you have ULN2803, you can use those as well, they are fairly good till almost 1A, if i recall correctly

Just crosschecked, ULN2803a are rated for 500ma

 

[bishoptf]

yeah, i think thats not a power mosfet. Logic level power mosfets look beefier, TO-220 packaging instead of TO-92. If you have ULN2803, you can use those as well, they are fairly good till almost 1A, if i recall correctly

Thanks, looks like I will be making a trip back to the store, lol. I think those are the pricer ones, they wanted $4 each for them, he did ask me what I intended to do with them and I wasn't sure, so power it is. I will get the TO-220 ones this time. I only need one per led unit, right?

 

[bishoptf]

Just crosschecked, ULN2803a are rated for 500ma

OK, according to that article the IRLB8721 are rated for 60a, I don't need any where close to that but he will know if they have something that will work that is lower. I would think anything that could handle 5-10 should be plenty. Looks like if I want to go cheaper then Tip-120 would also work, they can handle 5 amps.

 

[Ranjib]

Thanks, looks like I will be making a trip back to the store, lol. I think those are the pricer ones, they wanted $4 each for them, he did ask me what I intended to do with them and I wasn't sure, so power it is. I will get the TO-220 ones this time. I only need one per led unit, right?

they should be within 2$. Mine ones cost .75$ . Tell them you want a logic level N channel power mosfet. Logic level means the mosfet can be controlled by logic level voltage (3.3-5 v ), found in most microcontroller, power mosfet means they are optimized for exactly this type of use case.

 

[Ranjib]

OK, according to that article the IRLB8721 are rated for 60a, I don't need any where close to that but he will know if they have something that will work that is lower. I would think anything that could handle 5-10 should be plenty.

Its bit more complicated than that. You should ideally look for watts. which is volt x amp . So, at lower volts they can support higher amps. Its best to use dedicated mosfets per channel if possible. The overall watt used is also helpful in deriving whether you need a heatsink or not.

 

[theatrus]

Its bit more complicated than that. You should ideally look for watts. which is volt x amp . So, at lower volts they can support higher amps. Its best to use dedicated mosfets per channel if possible. The overall watt used is also helpful in deriving whether you need a heatsink or not.

Looking at max power dissipation is important, but sometimes isn't specified since it depends on thermal mounting. Calculating can be harder as well.

The first rule of MOSFETs is to never use them in the linear region - but with a logic level MOSFET and digital on/off control there is no risk there (there are linear FETs - rare and $$).

If you are just switching something on or off infrequently, you can generally ignore the on/off region of the switching time and just look at the MOSFET Rds(on). When fully switched on, a MOSFET acts like a resistor with the specified Rds(on) value. Note that Rds(on) can change quite a bit with gate voltage, so look for curves. Even logic level FETs may only have the lowest on resistance when the gate is above 5V.

If you're using them in a rapid PWM fashion, you need to count the time the MOSFET is transitioning between states (where its in a linear region, and power dissipation can be extremely high for short periods of time), which can vary how hard its driven, and if there is any ringing or other oscillations on the gate. This is hard to measure without proper tools and can be a bear to accurately simulate, so my rule of thumb is to healthily derate current/power by at least 50% when considering PWM applications for a FET.

 

[bishoptf]

Looking at max power dissipation is important, but sometimes isn't specified since it depends on thermal mounting. Calculating can be harder as well.

The first rule of MOSFETs is to never use them in the linear region - but with a logic level MOSFET and digital on/off control there is no risk there (there are linear FETs - rare and $$).

If you are just switching something on or off infrequently, you can generally ignore the on/off region of the switching time and just look at the MOSFET Rds(on). When fully switched on, a MOSFET acts like a resistor with the specified Rds(on) value. Note that Rds(on) can change quite a bit with gate voltage, so look for curves. Even logic level FETs may only have the lowest on resistance when the gate is above 5V.

If you're using them in a rapid PWM fashion, you need to count the time the MOSFET is transitioning between states (where its in a linear region, and power dissipation can be extremely high for short periods of time), which can vary how hard its driven, and if there is any ringing or other oscillations on the gate. This is hard to measure without proper tools and can be a bear to accurately simulate, so my rule of thumb is to healthily derate current/power by at least 50% when considering PWM applications for a FET.

Thanks this is good information, one of my concerns is the amp draw over the wiring, I would like to use the existing 12v input, I have a PS that is rated for 5amps @12v and if I do the math correctly if both light were to be on the highest setting they would pull 3.75amps (45w/12v=3.75). The small light is 12w and the larger one is 33w according to the information, I never run them at highest setting in fact the highest setting for me will be 50% but I still want to have some headroom if something were to happen and they both run at the highest setting.

The IRLB8721 https://www.adafruit.com/product/355 look like they are good for high power which would easily work and it appears that I could go with TIP-120 https://www.adafruit.com/product/976 they appear to be good for 5amp of continuous power. Will be heading to the store with more knowledge and hopefully get the correct parts. :)