Aux input (voltage to input) Megajolt v4 jr

General Topics for configuring, operating and tuning the Megajolt. Also see the <a href="http://www.autosportlabs.net/MJLJ_V4_Operation_Guide">Operation Guide</a>

Moderators: JeffC, rdoherty, stieg, brentp

Post Reply
pickle
Posts: 5
Joined: Mon May 17, 2010 10:52 pm

Aux input (voltage to input) Megajolt v4 jr

Post by pickle »

Hiya guys, great site! :D

I have a metro turbo engine, I am planning on using the engine coolant temp for the aux input on my v4 jr. The coolant sensor is 12v, will I have to try to reduce the voltage before it reaches the mj or is the mj regulated inside somwhere??

i have searched but cant find this out!

Any help greatly appreciated,

Thanks, Rich
megajolt baby!!!

BRUCEROE
Posts: 96
Joined: Wed Mar 03, 2010 10:00 pm

Temp Sensor

Post by BRUCEROE »

The MJLJ has an internal 2.2K pullup resistor to internal 5V. It can be calibrated to use a standard EFI temperature sensor. Is your present sensor already in use in the car; sensors don't have an internal voltage? Adding another might be the easiest. Bruce Roe

brentp
Site Admin
Posts: 6274
Joined: Wed Jan 24, 2007 6:36 am

Post by brentp »

Hi Rich,

What type of temperature sensor do you have? Almost all temperature sensors are passive 1 or 2 wire type. with the one wire type the 2nd wire is the body of the sensor, which is grounded. 2 wire types have the 2nd wire grounded as well- preferably to the same location where the sensing unit (i.e. megajolt) is grounded.

Here's the installation guide which illustrates how to wire the sensor.

http://www.autosportlabs.net/MJLJ_V4_ve ... e_resistor
Brent Picasso
CEO and Founder, Autosport Labs
Facebook | Twitter

pickle
Posts: 5
Joined: Mon May 17, 2010 10:52 pm

Post by pickle »

Hi guys, cheers for replies, I have a one wire type sensor and it is already in use, its powered down from 12v to 10v by a voltage regulator (thats what I meant by 12v sensor)
So would it be ok if I connect the aux input wire to the temp sensor aswell like below?

Thanks, Rich
Attachments
aux input.JPG
aux input.JPG (13.32 KiB) Viewed 14184 times
megajolt baby!!!

BRUCEROE
Posts: 96
Joined: Wed Mar 03, 2010 10:00 pm

Temp Sensor

Post by BRUCEROE »

That would NOT be OK, for a couple of reasons. The 2.2K resistor in the MKLJ would throw off your present circuit. Even if the 2.2K were disconnected, it is likely your present circuit sometimes exceeds 5 volts at the sensor. The MJLJ can't be calibrated outside of 0 to 5 volts. But connecting a second EFI style temp sensor to the MJLJ would solve the problem. You would still need to enter a calibration chart into the MJLJ for a degrees readout, but I have made one available for degrees F. Bruce Roe

pickle
Posts: 5
Joined: Mon May 17, 2010 10:52 pm

Post by pickle »

Thats what I wasnt sure about. I'll plumb in another water temp sensor somewhere and put the megajolt to that.. If I find that the sensor in the pic above does only recieve 5v max from the gauge I could still use it then couldnt I? but oly if it revieves 5v MAX!!

At the moment my aux input temp gauge is shownig the ADC value as the temp reading, by recalibrating it, you mean change the ADC value to degrees F or C so it shows as the degrees equilavant of the voltage reading on the gauge instead of the current ADC value? Whats the scaled value section for?

Is there a link to the one you have available in degrees F?

Thanks Rich
megajolt baby!!!

brentp
Site Admin
Posts: 6274
Joined: Wed Jan 24, 2007 6:36 am

Post by brentp »

As Bruce indicated has supplied us a calibrated temperature file for the GM sensor (thanks!) I have yet to add it to the wiki (on the list!) Bruce, could you attach it to this thread?
Brent Picasso
CEO and Founder, Autosport Labs
Facebook | Twitter

BRUCEROE
Posts: 96
Joined: Wed Mar 03, 2010 10:00 pm

Post by BRUCEROE »

If you use your present sensor (which NEVER exceeds 5V), you will have to measure the voltage and temperature (trust your original gauge?) over the operating range. Then make a conversion table for the MJLJ. Without a conversion chart the MJLJ gauge will apparently be reading backward. And disconnect the 2.2K resistor.

This is quite a project, that's why I suggest just simply adding a standard sensor & loading an existing table. I'll need to look up the sensor data sheet, from which I did a conversion chart. The sensor isn't linear with temperature, but resistance vs temp is on its data sheet. The resulting voltage with 5V applied to the 2.2K resistor can be calculated. Those voltages then make a table that the MJLJ translates from voltage input to degrees F at the on screen gauge. Guess you could do degrees C, but I believe the range of the readout is presently limited to 0 to 255. Bruce

pickle
Posts: 5
Joined: Mon May 17, 2010 10:52 pm

Post by pickle »

Ok thanks, i'll add another standard sensor for the mj. Lookin forword to seeing the data sheet,

Thanks, Rich
megajolt baby!!!

BRUCEROE
Posts: 96
Joined: Wed Mar 03, 2010 10:00 pm

Post by BRUCEROE »

Here is the generic temp sensor with resistance every 5 deg C; thats every 9 deg F. I figured the voltage with a 5V source through the MJLJ 2200 ohm series resistor every 9 deg F, extrapolated between. Below is MJLJ conversion table. Bruce Roe

http://www.pe-ltd.com/Downloads%5Ccoolant_temp.pdf


255
255
255
255
255
255
255
255
255
255
255
250
245
240
235
230
225
221
217
213
210
207
204
201
198
195
193
190
188
186
184
182
180
178
176
175
173
172
170
168
166
165
164
162
161
159
158
157
155
154
152
151
149
148
147
146
145
143
142
141
140
139
138
137
136
135
134
133
132
131
130
129
128
127
126
125
125
124
123
122
121
120
119
119
118
117
116
116
115
114
113
113
112
111
111
110
109
108
107
106
106
105
104
104
103
102
102
101
100
99
99
98
97
97
96
95
95
94
93
93
92
91
90
90
89
89
88
88
87
87
86
85
85
84
83
83
82
81
81
80
79
79
78
78
77
76
76
75
74
74
73
72
72
71
70
70
69
68
68
67
66
66
65
64
64
63
62
62
61
60
59
59
58
57
57
56
55
55
54
53
53
52
51
51
50
49
48
48
47
46
46
45
44
43
43
42
42
41
40
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
12
11
10
9
7
6
4
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

BRUCEROE
Posts: 96
Joined: Wed Mar 03, 2010 10:00 pm

Post by BRUCEROE »

If I had your email, I could send the conversion table as a .txt
file. For some reason, my APPLE doesn't like to deal with .txt
files. Or brentp can make it available.

Here is my translation from temperature degrees F to
voltage into MJLJ, with a 2200 ohm pullup resistor to 5.00V.
This circuit is shown on the sensor data sheet. It is best
to bring both sensor leads directly to the MJLJ. Grounding
the sensor to the block can introduce ground loop errors.

degC degF ohms volts
-40 -40 102,122 4.896
-35 -31 73,340 4.854
-30 -22 53,249 4.802
-25 -13 39,064 4.733
-20 -4 28,939 4.647
-15 5 21,637 4.539
-10 14 16,321 4.406
-5 23 12,413 4.247
0 32 9516 4.061
5 41 7354 3.849
10 50 5728 3.613
15 59 4496 3.357
20 68 3555 3.089
25 77 2830 2.813
30 86 2268 2.538
35 95 1828 2.269
40 104 1483 2.013
45 113 1210 1.774
50 122 992 1.554
55 131 819 1.356
60 140 679 1.179
65 149 566 1.023
70 158 475 0.888
75 167 400 0.769
80 176 338 0.666
85 185 287 0.577
90 194 244.8 0.501
95 203 209.7 0.435
100 212 180.3 0.379
105 221 155.6 0.330
110 230 134.7 0.288
115 239 117.1 0.253
120 248 102.2 0.222
125 257 89.4 0.195
130 266 78.5 0.172
135 275 69.1 0.152
140 284 61.1 0.135
145 293 54.1 0.120
150 302 48.1 0.107

Since the MJLJ currently can only display numbers between 0
and 255, the conversion table must be limited to that range.
I just extrapolated the in between degree F values. A translation
table for degrees C will only be able to go down to water freezing.
Bruce Roe

pickle
Posts: 5
Joined: Mon May 17, 2010 10:52 pm

Post by pickle »

Thanks BRUCEROE,

I will use your translation and add my own extrapolated values in between..
I will update this and let you know how it goes when I get a chance to do the chart and get on my mj and fiddle.

Thank you loads and loads :D

Rich
megajolt baby!!!

alhbln
Posts: 29
Joined: Sat May 31, 2008 3:40 pm
Location: Germany
Contact:

Re: Temp Sensor

Post by alhbln »

BRUCEROE wrote:That would NOT be OK, for a couple of reasons. The 2.2K resistor in the MKLJ would throw off your present circuit. Even if the 2.2K were disconnected, it is likely your present circuit sometimes exceeds 5 volts at the sensor. The MJLJ can't be calibrated outside of 0 to 5 volts. But connecting a second EFI style temp sensor to the MJLJ would solve the problem. You would still need to enter a calibration chart into the MJLJ for a degrees readout, but I have made one available for degrees F. Bruce Roe
How about adding a simple high resistance voltage divider (e.g. 14K/10K) to the Megajolts Aux input, which lowers the output from the temperature sensor to a safe 0-5V TTL signal? That shouldnt interfere with the Temperature Gauge (at least not more than 5-10%, which you wouldn't notice on the 240Z gauge anyway) and you could leave the factory temperature sensor and gauge in place.
Attachments
vdivider.png
vdivider.png (7.55 KiB) Viewed 13971 times

BRUCEROE
Posts: 96
Joined: Wed Mar 03, 2010 10:00 pm

Voltage Divider

Post by BRUCEROE »

That will work. But then there is still the problem of generating a calibration chart for the original gauge-sensor combination, how do you do that? Also, 12V to the gauge varies a lot from say, idle with lights on, to full speed no load. That voltage variation will cause the MJLJ gauge to change every time you step on the gas, because the MJLJ reference voltage is fixed. The original gauge probably has compensating circuitry.

A divider with high enough impedance to not affect the original circuit, will not be able to drive much voltage into the 2.2K MJLJ pullup resistor. So the 2.2K will need to be disconnected for decent resolution. Not needed for separate sensor.

Bruce Roe

alhbln
Posts: 29
Joined: Sat May 31, 2008 3:40 pm
Location: Germany
Contact:

Re: Voltage Divider

Post by alhbln »

BRUCEROE wrote:That will work. But then there is still the problem of generating a calibration chart for the original gauge-sensor combination, how do you do that? Also, 12V to the gauge varies a lot from say, idle with lights on, to full speed no load. That voltage variation will cause the MJLJ gauge to change every time you step on the gas, because the MJLJ reference voltage is fixed. The original gauge probably has compensating circuitry.

A divider with high enough impedance to not affect the original circuit, will not be able to drive much voltage into the 2.2K MJLJ pullup resistor. So the 2.2K will need to be disconnected for decent resolution. Not needed for separate sensor.

Bruce Roe
Voltage variation is a good point, i am just trying to avoid to drill a hole in my engine block. I guess i'll have a look at the gauge itself, there might be a chance to get a voltage output after the line regulator.

Good input, thanks!

Post Reply