HM 4-Line LCD build for electric smoker


 
T

Tony L-Iowa

TVWBB Fan
I have put together my first A+/HM 4-line LCD unit. Haven't found any issues issues yet. I've quickly hooked up and viewed data for the ambient thermistor, 2 probes and 1 thermocouple. Next steps are case mounting (when it arrives), and electric smoker modifications to my Smokin-It Model #2. I'm doing a permanent mount thermocouple in the smoker and installing a Solid State Relay (SSR) for the HM to control my smoker heating element. I really appreciate all the hard work and thought that have been put into this project. The forums, wiki, schematics, circuit boards, cases, and materials are all TOP NOTCH! Keep up the good work as I believe you have something better than the Auber PID here. It's very close cost wise and the HM wins with features and coolness factor IMHO!

I was powering this thing from the USB port at first. I measured about 110 mA current draw from the 12VDC connector with my multimeter (with just LCD on @50% and only thermocouple plugged in). Are 12VDC truely required at the connector? Would I be able to take a 4-pack of NiMH AAA or AA (~1.2volt 1000mah or 2400mah) batteries and power this thing without the AC<->12VDC power supply?

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You can run the HM on 5V if you don't use the blower, but in your case even though you are not using a blower you would be using the blower output to control the SSR. IDK what the blower circuit does when you only feed it 5VDC TBHWY. If it continues to function but at a lower voltage you might still be able to make it work to flip the right SSR.... You would have to use PULSE mode for the blower rather than Voltage mode....
 
The blower output wouldn't be powered at all if you don't plug in the 12V jack. You could always plug 5V in there too. The current draw you're measuring is before the switching regulator which is about 80% efficient though so roughly double current draw that if you're running from 5V.

You're may be better way better off getting a 12V battery from a UPS or something because you get the benefit of the step down regulator and have one power input. I've run it up to 20V input and it works fine, as long as your SSR is rated for the 12V battery voltage (~13.7V).
 
My SSR from Amazon is rated on the input side from 3-32VDC. I was considering making a 4 or 8 pack that plugs into the jack. Well, this is a cheap one I just found on Amazon. 8 pack would be really close to 12VDC. What's the minimal input voltage for this thing to run?
 
The input voltage is rated 7-36V, however I'd recommend keeping it below 20V. If you try running HeaterMeter on AA batteries, make sure you check back in, I am curious how much life you can get out of them!
 
Bryan Mayland said:
The input voltage is rated 7-36V, however I'd recommend keeping it below 20V. If you try running HeaterMeter on AA batteries, make sure you check back in, I am curious how much life you can get out of them!
Click to expand...

I ordered the 2.1x5.5mm Plug Batteries Case Box w Cover for 8 x 1.5V AA Battery and did a HM battery test today. I smoked spare ribs and kept the HM on battery power ~7.2 hours (outside temp ~10ºF). I only had one probe hooked up to monitor the the internal smoker temp. I had 8 brand new AA NiMH batteries (Powerex 2700mah/2500mah minimum). I broke the batteries in with my MH-C9000 charger before the test and measured the charge capacity on each battery before the test. I will use the same charger to report how much capacity they accept on a follow-up recharge.

I should note I had LCD backlight at 3% for ~5 hours and 50% ~2 hours. Had client(s) connected to web interface almost 100% of the time to monitor.

Start (8-pack) combined voltage = 11.03V
Battery 1 capacity = 2553 mAh
Battery 2 capacity = 2529 mAh
Battery 3 capacity = 2522 mAh
Battery 4 capacity = 2484 mAh
Battery 5 capacity = 2532 mAh
Battery 6 capacity = 2528 mAh
Battery 7 capacity = 2552 mAh
Battery 8 capacity = 2508 mAh

Finish (8-pack) combined voltage = 10.36V
(recharged at 1300mAh via MH-C9000)
Battery 1 capacity accepted via recharge = 834 mAh
Battery 2 capacity accepted via recharge = 895 mAh
Battery 3 capacity accepted via recharge = 909 mAh
Battery 4 capacity accepted via recharge = 868 mAh
Battery 5 capacity accepted via recharge = 772 mAh
Battery 6 capacity accepted via recharge = 826 mAh
Battery 7 capacity accepted via recharge = 840 mAh
Battery 8 capacity accepted via recharge = 804 mAh

Overall I think the battery pack worked pretty good. It sat nicely on my smoker as follows:
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Along similar lines to this, if you've got 18v power tools, you should be able to directly power the HM with it.

We had the power go out last night for almost 10 hours and I was thinking of alternate ways to charge and/or power USB devices and it occurred to me that I already had the parts.

I have an abundance of these cigarette lighter USB chargers from trade shows. Some quick testing showed they handle the 18v input from my power tool battery just fine. Bingo bango, gobs of USB power available!

 
You know, with all the gadgets we have around today you can Macgyver just about anything if you think hard enough! This ones pretty cool...
I wonder how long you could run a HM on a drill battery? I bet pretty long...The OKI regulator in the HM can handle up to 36v so all the 3.3 an 5V stuff would be fine, I wonder how the blower circuit would react to 18VDC?
 
I've often wondered why there isnt a 12V regulator on the HM board.... Seems since wall warts vary so much it would be best to start right off the bat with a 12V regulator to make the whole thing more stable and standard....
 
Well you gotta feed some sort of power into the thing, and I wouldn't feel comfortable with a board that's designed for novices to put together that you feed mains voltage into. Given that you have to feed something in, it might as well be 12VDC.

The blower circuit works fine with higher voltages too because it is a 62Khz switching regulator (although it doesn't regulate as quickly as a dedicated regulator). I forget how high I've run the input voltage but I think 20VDC worked fine with the standard blower current draw. An LM7812 would be a waste because both the 5V regulator and blower circuit pull less current the higher the voltage is so if you use a linear regulator it will just waste that as heat.

The reason I don't use a TO220-5 switching regulator instead of the Murata unit is that you still have to add a diode and inductor and now you're using a bunch of board space and saving very little in terms of cost and may perform worse because the components aren't matched.
 
Well, I don't get the comment about the mains voltage, I wasn't suggesting supplying mains voltage to the board (maybe someone else did and I missed it?)
I was suggesting, since we already have the fairly large and expensive OKI DC-DC converter to provide 5v and a 3.3v regulator on the board, it might be better to use that switching regulator that can take in up to 30VDC and output 12v,5v,3.3v. It's all in one package that looks to be about the size of the blower MOSFET.
 
I'm confused because the part you linked is a single output switching regulator which needs an external diode, feedback resistors, and pricey beefy inductor. The part by itself is larger than the Murata (if horizontally mounted). But you would need 3 sets of components to generate 3 voltages.

The current setup can take over 20VDC and only has $4.77 (quantity 1) worth of voltage regulators. Two of those parts are already over that without the external components. I feel like this already is the best solution functionally, board space, and cost-wise (although that is a tossup) apart from SMD.
 
Ok, got me there, I didn't look into the fact that you need 3 sets of external components to regulate the three output voltages... My point in general was 12VDC wall warts vary greatly in both their output voltage and stability, and it seems to effect the noise levels and stability of temperature readings on the HM quite a bit... So it seems to me it might be better to start out regulating the 12VDC to some reliable standard on the HM board to make it more forgiving of the wall wart issue. The part I linked looked (falsely) like a simple solution to accomplish this, though I didn't put my finger on the proper part first time around I still feel the HM should clean up the 12VDC on the way in some way or other...
 
RalphTrimble said:
I still feel the HM should clean up the 12VDC on the way in some way or other...
Click to expand...
It's not so much the 12V we're worried about but what happens on the 3.3V line coming from noise that loops through the whole system. That's why 5.0 is still on rev 0, because I am experimenting with various methods of reducing it. It is pretty difficult though because I have what at the time was the world's cheapest digital scope and also because I am not an Electrical Engineer. There's already split ground planes and dedicated "no cross" areas, and the atmel recommended inductor on the analog power and separate analog decoupling caps... then I added a bunch of other parts to see if I could get it to be completely flat. Ironically now the largest power spike is when you switch analog voltage references. I'd still like to improve it further and still have to do comparison testing. I'd like it to be as noise free as a battery-powered probe but I doubt I'll be able to.

Also the linked regulator doesn't just need 3 sets of external components, it needs 3 regulators. It is single output. The extra pins are for the extra parts you need to make it work.

EDIT: But the part that's garbage usually isn't the 12V portion, it some manner of ground isolation in the wall wart which we can't fix by putting another regulator in between.
 
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FYI - My Raspi Model A+ test completed. It remained powered on with a Ryobi 18v model P104 battery for 17.7 hours. It would have been sitting idle, at about 100ma draw.

Using an assumed power factor of 0.7, that puts it at about 2500 mAh
 
I know the power consumption on the HM is hard to predict, but I'm thinking perhaps that battery might work long enough to do some ribs or maybe a pork shoulder? Would need a couple to do a brisket thats for sure... I really like the idea of running the HM off a drill battery, 'cause most of us prob have a cordless drill, so we already own them... and I doubt too many of us are drillin' and grillin' at the same time.... lol
 
I've got my HM in manual fan mode, set to 40%

I'm sending an update to thingspeak.com every minute with the system uptime in minutes.

You can see it here.

Should be a good baseline to see how long it will last in a real cook.

Code: 
# crontab -l
* * * * *  /mnt/mmcblk0p4/uptime.sh

# cat /mnt/mmcblk0p4/uptime.sh 
#!/bin/sh

uptime=$(awk -F. '{print $1}' /proc/uptime)
minutes=$(( uptime/60 ))

TYPE="Content-Type: application/json"
TOKEN="X-THINGSPEAKAPIKEY: XXXXXXXXXXXX"
URL="https://api.thingspeak.com/update.json"
PAYLOAD=$(echo {\"field1\":$minutes})

curl -k -m 40 -o /dev/null -s -H "$TYPE" -H "$TOKEN" -d "$PAYLOAD" "$URL"
 
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